CONTENTSSr. No Topic Page No.

1 About Team RPM 4 2 Increasing Engine Power Output Back Pressure and Velocity 6

Exhaust Theory 8

Engine Performance 12

Collector 13

Header 14

Mufflers 15

Hypereutectic Piston 20

Stage One Modifications 21

3 Esteem VXI BSIII Tech. Spec. 23

4 SOHC Valve Mechanism DOHC 25

3 Stage V-Tec 27

i-VTec 29

5 Braking System

Drum Brake 31

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Disc Brake 34

Run Out 37

6 In Line Cylinder Configuration Piston Speed 41

Balance Shaft Use 42

7 Electronic Control Module (ECM) Working of ECU 45

Programmable ECU’s 47

8 Air Intake System Air Filter 51

Mass Flow Sensor 53

Throttle Body 56

Cold air Intake 58

9 Existing Exhaust System 59 10 Turbochargers Twin Turbo 70

Intercooling 71

11 Automotive Aerodynamics

Measuring Drag 73

Spoilers 75

12 Differential 78

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13 Fuel Injection System

14 Cost Sheet 15 Performance Charts 16 Conclusion

About Team RPM

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INCREASE ENGINE POWER OUTPUT

1. Change your computer chip. Sometimes, but certainly not always, you can change a car's performance by changing the ROM chip in the engine control unit (ECU). You usually buy these chips from aftermarket performance dealers. It is valuable to

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read an independent review of the chip you are contemplating, because some chips are all hype and no performance.

2. Let air come in more easily. As a piston moves down in the intake stroke, air resistance can rob power from the engine. Some newer cars are using polished intake manifolds to eliminate air resistance there. Bigger air filters and reduced intake piping can also improve air flow.

3. Let exhaust exit more easily. If air resistance or back-pressure makes it hard for exhaust to exit a cylinder, it robs the engine of power. If the exhaust pipe is too small or the muffler has a lot of air resistance then this can cause back-pressure. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system. Air resistance can be lessened by adding a second exhaust valve to each cylinder (a car with two intake and two exhaust valves has four valves per cylinder, which improves performance). If the exhaust pipe is too small or the muffler has a lot of air resistance, this can cause back-pressure, which has the same effect. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system.

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pulses and so on. The more pulses that are produced, the more continuous the exhaust flow. Back pressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

Back pressure and velocity

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Many people mistakenly believe that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this idea would be appealing - as wider pipes have the capability to flow more than narrower pipes. However, this omits the concept of exhaust VELOCITY. Here is an analogy...a garden hose without a spray nozzle on it. If you let the water just run unrestricted out of the hose it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will spray out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. (see below) If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be travelling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you also want make sure the pipe is wide enough so that there is as little back pressure as possible while maintaining suitable exhaust gas velocity.

Many engineers try to work around the RPM specific nature of pipe diameters by using set-ups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb back pressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

How did the myth about back pressure and big pipes come to be?

It is believed as a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a Honda Civic decides he's going to upgrade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the power band. He makes the connections in the following manner: "My wider exhaust eliminated all back pressure but I lost power, therefore the motor must need some back pressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero back

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pressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

A header (aka branch manifolds or extractors) is a manifold specifically designed for performance. Engineers create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. These designs can  result in more efficient scavenging of the exhaust from the cylinders. Headers are generally circular steel or stainless tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not backwards towards the other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in particular engine revolutions per minute range and married to the firing sequence.Inefficiencies generally occur due to the nature of the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates back pressure and restriction in the engine's exhaust system and limits the engine's true performance possibilities.

Q). Why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this article but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle travelling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).Many designers will increase the length of the exhaust, trying to achieve a faster flow and a larger area of low pressure. Short pipes create a smaller low pressure area.

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Exhaust theory

In order to explain the effect of exhaust tuning on performance, let’s take a quick look at the 4-stroke engine cycle.  The first step in the 4-stroke process is the intake stroke.  With the intake valve open, the piston travels down the cylinder pulling a fresh air and fuel mixture into the cylinder (intake stroke).  When the piston nears bottom dead center, the intake valve closes and the piston travels up the cylinder compressing the air/fuel charge (compression stroke).  With the piston at the top of the stroke, the spark plug fires and ignites the compressed mixture causing essentially a closed explosion.  The pressure of the ignited fuel pushes the piston down the cylinder transferring power to the piston, rod and finally the crankshaft (power stroke).  After bottom dead center, the exhaust valve opens and the piston is pushed up the cylinder forcing the exhaust gases out the exhaust port and manifold (exhaust stroke).

As the exhaust valve opens, the relatively high cylinder pressure (70 – 90 psi), initiates exhaust blowdown and  a large pressure wave travels down the exhaust pipe.  As the valve continues to open, the exhaust gases begin flowing through the valve seat.  The exhaust gases flow at an average speed of over 350 ft/sec, while the pressure wave travels at the speed of sound of around 1,700 ft/sec.As one can see, there are two main phenomenons occurring in the exhaust, gas particle flow and pressure wave propagation.  The objective of the exhaust is to remove as many gas particles as possible during the exhaust stroke.  The proper handling of the pressure waves in the exhaust can help us to this end, and even help us “supercharge” the engine.As the exhaust pressure wave arrives at the end of the exhaust pipe, part of the wave is reflected back towards the cylinder as a negative pressure (or vacuum) wave.  This negative wave if timed properly to arrive at the cylinder during the overlap period can help scavenge the residual exhaust gases in the cylinder and also can initiate the flow of intake charge into the cylinder.  Since the pressure waves travel at near the speed of sound, the timing of the negative wave can be controlled by the primary pipe length for a particular rpm. 

The strength of the wave reflection is based on the area change compared to the area of the originating pipe.  A large area change such as the end of a pipe will produce a strong reflection, whereas a smaller area change, as occurs in a collector, will produce a less-strong wave.  A 2-1 collector will have a smaller area change than a 4-1 collector producing a weaker pressure wave.  Also, a merge collector

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will have a smaller area change than a standard formed collector producing a weaker wave.When considering a header design, the following points need to be considered: 

1) Header primary pipe diameter (also whether constant size or stepped pipes).  2) Primary pipe overall length. 3) Collector package including the number of pipes per collector and the outlet sizing.4) Megaphone/tailpipe package.

An example of megaphone silencer….. for reducing back pressure, for efficient sending of the pressure waves back towards the cylinder.

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How Does an Exhaust System Improve the Power Output of an Engine?

In the simplest terms, it increases the mass airflow through the engine by improving the volumetric efficiency (VE) of the engine and by reducing pumping losses on the exhaust side.

Volumetric efficiency is defined as the actual volume of air that the engine captures in its cylinders divided by the physical size of the swept volume of the cylinder and combustion chamber. In other words, if a cylinder has a swept volume of 37.5 ci and it only pulls in 18.75 ci, we say it is 50 percent volumetric efficient; for 100 percent VE, it'd take in 37.5 ci.

Pumping losses refer to the power used to pump the mass in and out of the engine. A portion of the engine's power is used to generate a pressure drop in the cylinder on the intake stroke that is filled to the extent of the cylinder's volumetric efficiency by the higher pressure of atmosphere (about 14.7 psi at sea level for standard conditions). A portion of the engine's power is also used to force the leftover gas

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from the combustion process, out of the combustion chamber, through the exhaust port, down the exhaust system, and finally, out into the pressure of the atmosphere.

Which Header Design Makes Most Power?

A 4-into-1 header with a fine-tuned collector tends to create the most peak power of any header design. To make this design work, you have to introduce the primary tubes into the collector stacked: two on the top, two on the bottom. It doesn't work if you collect the tubes side by side; this causes ground clearance and routing problems for some vehicles. The next best solution is a 4-2-1 design, which gives more ground clearance as well as requiring less room to route through tight engine compartments. The downside is you loose a little power. When matched with the properly sized tube diameters and length for your combination, you're typically within about 3 to 5 hp, depending on engine size, of what a similarly matched 4-into-1 system would do.

Whether it's a 4-2-1 or a 4-into-1 header, the basic tuning theory of small-diameter long tubes for torque and larger-diameter short tubes for high-rpm horsepower typically holds true. However, there are always exceptions, especially with 4-2-1 headers because you have the secondary tubes to play with as well as the primaries.

Shorty headers are generally better than stock, but be very careful when choosing this design for a modern engine. The factories are designing very efficient engines with equally efficient exhaust systems.

Ultimately, an exhaust header can only be tuned to be really effective within a fairly narrow rpm range, say around 1,000 rpm. So you need to choose a header design that works with your combination. For example, don't use headers tuned to make power at 3,000 rpm if your engine has a wicked mega-duration, high-lift, high-rpm cam with head porting.

Relation between engine rpm and vehicle speed in miles/hour

(0.00595) * (RPM * r) / (R1 * R2) = vehicle speed in miles/hour

    where:            RPM = engine speed, in revolutions/minute           r = loaded tire radius (wheel center to pavement), in inches           R1 = transmission gear ratio           R2 = rear axle ratio

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How do exhaust headers work to improve engine performance?Headers are one of the easiest bolt-on accessories you can use to improve an engine's performance. The goal of headers is to make it easier for the engine to push exhaust gases out of the cylinders.The engine produces all of its power during the power stroke. The gasoline in the cylinder burns and expands during this stroke, generating power. The other three strokes are necessary evils required to make the power stroke possible. If these three strokes consume power, they are a drain on the engine.

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve opens at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted. Using two exhaust valves rather than one improves the flow by making the hole that the exhaust gases travel through larger.

In a normal engine, once the exhaust gases exit the cylinder they end up in the exhaust manifold. In a four-cylinder or eight-cylinder engine, there are four cylinders using the same manifold. From the manifold, the exhaust gases flow into one pipe toward the catalytic converter and the muffler . It turns out that the manifold can be an important source of back pressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold.

The idea behind an exhaust header is to eliminate the manifold's back pressure. Instead of a common manifold that all of the cylinders share, each cylinder gets its own exhaust pipe. These pipes come together in a larger pipe called the collector. The individual pipes are cut and bent so that each one is the same length as the others. By making them the same length, it guarantees that each cylinder's exhaust gases arrive in the collector spaced out equally so there is no back pressure generated by the cylinders sharing the collector.

Many stock exhaust systems are not capable of transferring sufficient exhaust gas at high engine speeds. Restrictions to this flow can include exhaust manifolds, catalytic converters, mufflers, and all connecting pipes routing combustion residue away from the engine.

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Combustion by-products won't burn a second time. Therefore, an exhaust system that cannot properly rid cylinders of exhaust gas can cause contamination of fresh air/fuel charges. Residual exhaust material occupies space in the cylinders that prevents maximum filling during inlet cycles. As a rule, this problem grows with rpm, potentially reducing the benefits that can be derived from other performance-enhancing parts.As you will see, exhaust-flow velocity is an important component in an efficient exhaust system. Simply stated, at low rpm, the flow rate tends to be slow.

In the case of headers, primary-pipe diameter determines flow rate (velocity). At peak torque (peak volumetric efficiency), the mean flow velocity is 240-260 feet per second (fps), depending upon which mathematical basis is used to do the calculation. But for sizing or matching primary pipes to specific engine sizes and rpm, 240 fps is a good number.

What Do Collectors Do?

Essentially, collectors have an impact on torque below peak torque. While the gathering or merging of primary pipes does affect header tuning, it is the addition of collector volume (typically changes to pipe length once a diameter is chosen) that alters torque. Engines operated above peak torque, particularly in drag racing, do not derive any benefit from collectors. Those required to make power in a range that includes rpm below peak torque do benefit. And the further below peak torque they are required to run (from 2,500-7,500 rpm for example), the more improvement collectors provide.

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Joining collectors, cross-pipe science notwithstanding, tends to further boost low-rpm torque by the increase in total collector volume. Generally, crossover pipes become less effective at higher rpm, as you might expect, although some manufacturers of the more scientific cross-pipes claim power gains as engine speed increases.

Header Size

Consider this: It is the downward motion of a piston that creates cylinder pressure less than atmospheric. Intake flow velocity then becomes a function of piston displacement, engine speed, and the cross-section area of the inlet path. On the exhaust side, a similar set of conditions exists. In this case, exhaust-flow velocity depends on piston displacement, engine speed, the cross-sectional area of the exhaust path, and cylinder pressure during the exhaust cycle.

Of the similarities between the intake and exhaust process, piston displacement, engine speed, and flow-path cross section are common. Therefore, there must be a functional relationship among rpm, piston displacement, and flow-path section area, and there is.

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Matching Headers to Objectives

If we know any two of the three previously mentioned variables (piston displacement, rpm, or primary-pipe diameter), we can apply some simple math to solve for the other. Here's how that works.

1. Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Given this relationship, we can perform some transposition to solve for the primary-pipe cross-section area.

Here's an example of how this approach can work. Suppose you have a 350ci small-block (43.75 cubic inches per cylinder). A primary-pipe torque boost around 4,000 rpm is your target engine speed. The choices for pipe size are 15⁄8 inches, 13⁄4 inches, and 17⁄8 inches. If we assume a tubing wall thickness of 0.040 inch, each of these od dimensions requires subtracting 0.080 inch when computing cross-section areas.

MUFFLERS

If you've ever heard a engine running without a muffler, you know what a huge difference a muffler can make to the noise level. Inside a muffler, you'll find a deceptively simple set of tubes with some holes in them. These tubes and chambers are actually as finely tuned as a musical instrument. They are designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out.

First we need to know from where the sound comes in an engine.

Where Does the Sound Come From?

In an engine, pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other. They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do.

It turns out that it is possible to add two or more sound waves together and get less sound.

It is possible to produce a sound wave that is exactly the opposite of another wave. If the two waves are in phase, they add up to a wave with the same frequency but twice the amplitude. This is

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called constructive interference. But, if they are exactly out of phase, they add up to zero. This is called destructive interference.

Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. Take a look at the inside of this muffler:

The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler.

A chamber called a resonator is connected to the first chamber by a hole. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound.

Waves cancelling inside a simplified muffler

In reality, the sound coming from the engine is a mixture of many different frequencies of sound, and since many of those frequencies depend on the engine speed, the sound is almost never at exactly the right frequency for this to happen. The resonator is designed to work best in the frequency range where the engine makes the most noise; but even if the frequency is not exactly what the resonator was tuned for, it will still produce some destructive interference. Some cars, especially luxury cars where quiet operation is a key feature, have

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another component in the exhaust that looks like a muffler, but is called a resonator. This device works just like the resonator chamber in the muffler -- the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.

There are other features inside this muffler that help it reduce the sound level in different ways. The body of the muffler is constructed in three layers: Two thin layers of metal with a thicker, slightly insulated layer between them. This allows the body of the muffler to absorb some of the pressure pulses. Also, the inlet and outlet pipes going into the main chamber are perforated with holes. This allows thousands of tiny pressure pulses to bounce around in the main chamber, cancelling each other out to some extent in addition to being absorbed by the muffler's housing.

Backpressure and Other Types of Mufflers

One important characteristic of mufflers is how much back pressure they produce. Because of all of the turns and holes the exhaust has to go through, mufflers like those in the previous section produce a fairly high backpressure. This subtracts a little from the power of the engine.

There are other types of mufflers that can reduce backpressure. One type, sometimes called a glass pack or a cherry bomb, uses only absorption to reduce the sound. On a muffler like this, the exhaust goes straight through a pipe that is perforated with holes. Surrounding this pipe is a layer of glass insulation that absorbs some of the

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pressure pulses. A steel housing surrounds the insulation

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A glass pack muffler

4. Change the heads and cams. Many stock engines have one intake valve and one exhaust valve. Buying a new head that has four valves per cylinder will dramatically improve airflow in and out of the engine and this can improve power. Using performance cams can also make a big difference.

5. Increase the compression ratio - Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline -- their engines are using higher compression ratios to get more power.

6. Stuff more into each cylinder - If you can cram more air (and therefore fuel) into a cylinder of a given size, you can get more power from the cylinder (in the same way that you would by increasing the size of the cylinder). Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder.

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7. Cool the incoming air - Compressing air raises its temperature. However, you would like to have the coolest air possible in the cylinder because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. An intercooler is a special radiator through which the compressed air passes to cool it off before it enters the cylinder.

8. Make everything lighter - Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes.

9. Using Forged Pistons and Connecting Rods : The difference between a cast and forged piston is the way it is made. A cast piston is made by pouring or injecting molten aluminum into a mold and letting it cool. A forged piston is made by ramming a die into a hot but not quite molten ingot of aluminum in a mold under great pressure (20+ tons!) The extreme pressure created in the forging causes the metal to be denser and have a uniform grain, making it much stronger and less brittle. There is more to making forged pistons than just the different manufacturing process, they often start with a stronger alloy such as 4032 or 2618 aluminum. Cast pistons are high in silicon content, which makes them dimensionally stable under high temperatures, but brittle. Forgings have a low silicone content and thus "grow" (expand) more when hot, but offer much improved strength and resiliency.

When auto enthusiasts want to increase the power of the engine, they may add some type of forced induction. By compressing more air and fuel into each intake cycle, the power of the engine can be dramatically increased. This also increases the heat and pressure in the cylinder.The normal temperature of gasoline engine exhaust is approximately 650 °C (1,200 °F). This is also approximately the melting point of most aluminium alloys and it is only the constant influx of ambient air that prevents the piston from deforming and failing. Forced induction increases the operating temperatures while "under boost", and if the excess heat is added faster than engine can shed it, the elevated cylinder temperatures will cause the air and fuel mix to auto-ignite on the compression stroke before the spark event. This is one type of engine knocking that causes a sudden shockwave

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and pressure spike, which can result in failure of the piston due to shock induced surface fatigue, which eats away the surface of the piston.The "2618" performance piston alloy has less than 2% silicon, and could be described as hypo (under) eutectic. This alloy is capable of experiencing the most detonation and abuse while suffering the least amount of damage. Pistons made of this alloy are also typically made thicker and heavier because of their most common applications in commercial diesel engines. Both because of the higher than normal temperatures that these pistons experience in their usual application, and the low-silicon content causing the extra heat-expansion, these pistons have their cylinders bored to very much cold-play. This leads to a condition known as "piston slap" which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures. These engines (even more so than normal engines) should not be revved when cold, or excessive scuffing can occur.The "4032" performance piston alloy has a silicon content of approximately 11%. This means that it expands less than a piston with no silicon, but since the silicon is fully alloyed on a molecular level (eutectic), the alloy is less brittle and more flexible than a stock hypereutectic piston. These pistons can survive mild detonation with less damage than stock pistons.CharacteristicsThe main characteristic that makes forged pistons excel in high performance applications is strength and durability. The high silicon content of cast pistons makes them brittle compared to forged pistons. Silicon gives the metal lubricity and is mixed in the alloy to limit heat expansion. This is primarily the reason why cast pistons require careful handling. Mild shock applied to it may cause the material to break. The process of forging compresses the molecules inside the alloy, which results in a denser surface area compared to a cast piston.It is true that forged pistons are heavier than cast pistons, but this is counteracted by the ability to provide a high compression ratio inside the engine, enabling the engine to rev higher and produce more power. Most turbocharged and high performance car models use forged pistons because they're more tolerant to the abuses of extreme heat, detonation and pressure inherent in performance oriented engines.An engine modification tweaked toward producing more power will benefit from a forged piston, as the high tolerance to abuse enables the tuner or engine builder to make incremental adjustments to

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enhance engine performance. Forged pistons are also readily available compared to cast pistons which are only available in OEM sizes, hampered by the expensive casting process.HYPEREUTECTIC PISTONA hypereutectic piston is an internal combustion engine piston cast using a hypereutectic alloy–that is, a metallic alloy which has a composition beyond the eutectic point. Hypereutectic pistons are made of an aluminum alloy which has much more silicon present than is soluble in aluminum at the operating temperature. Hypereutectic aluminum has a lower coefficient of thermal expansion, which allows engine designers to specify much tighter tolerances.The most common material used for automotive pistons is aluminum due to its light weight, low cost, and acceptable strength. Although other elements may be present in smaller amounts, the alloying element of concern in aluminum for pistons is silicon. The point at which silicon is fully and exactly soluble in aluminum at operating temperatures is around 12%. Either more or less silicon than this will result in two separate phases in the solidified crystal structure of the metal. This is very common. When significantly more silicon is added to the aluminum than 12%, the properties of the aluminum change in a way that is useful for the purposes of pistons for combustion engines. However, at a blend of 25% silicon there is a significant reduction of strength in the metal, so hypereutectic pistons commonly use a level of silicon between 16% and 19%. Special moulds, casting, and cooling techniques are required to obtain uniformly dispersed silicon particles throughout the piston material.Hypereutectic pistons are stronger than more common cast aluminium pistons and used in many high performance applications. They are not as strong as forged pistons, but are much lower cost due to being cast.

STAGE ONE MODIFICATIONS:Upgrade tyres and alloy wheels:Before adding more power to your car, it must have the adequate grip levels for current & future power delivery. Alloy wheels are not always necessary for a tyre upsize.

Tread PatternThe tread pattern of a tyre has a major effect on the tyres wet weather performance, which depends on its ability to channel water away from the contact patch between the tyre and the road. The tread pattern also plays a part in how much road noise is generated by the tyre due to air

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getting trapped and expelled from those channels during running. Tests have shown that the tread pattern of a tyre does not have as much of an effect as the compound of the tyre when it comes to traction, but nonetheless it plays a part. (Unless ofcourse you are looking at a tyre for mud, snow or sand, in which case the tread pattern plays a vital role.). Never buy re-treaded tyres; they are dangerous and not worth the little money you save.

Air-Filter:A stock replacement performance filter requires no modifications and is very simple to install since it fits exactly in place of your factory filter. The performance gains are marginal. A Cold air intake (CAI) is the more serious of performance air-filters. With a CAI, proper installation is very important and it should not suck in hot air. The colder the air available to it, the better will be the gains in performance. A true CAI sucks in outside air, while short rams and most CAI applications take air from under the hood. Even if it's 35 degrees outside, that is still significantly cooler than the air under your hood. You can also opt for a good conical / universal filter without CAI. The plumbing needs to have minimum restrictions with most experts recommending mandrel bent aluminium pipes. The diameter of the pipe through its entire length should be uniform and greater than that of the throttle body. Do note that the sound levels with significantly increase with a CAI, and some precautions must be taken when driving in the monsoons. K&N recommends a shroud for use in dusty conditions. 

Free-Flow Exhaust:A well-designed free flow exhaust system improves the breathing abilities of your engine and can lead to good performance / fuel-efficiency gains. It is important to get a complete free-flow kit (including headers) and not a muffler / end-can kit only. A good header design is very important and you may specify to your installer a preference of low, mid or high-rpm gains. Very little time is actually spent at high-rpm, so you might be better off asking for a low to mid-range power gain. The appropriate back pressure must be maintained else you will lose out on torque. An exhaust system is like a chain and only as strong as its weakest link. The most restrictive part is usually the cat-con or the mid-muffler. Some tuners will remove the cat-con, which will result in difficulty toward meeting the emission norms. Also, try and insulate the exposed part of the exhaust system within the hood with asbestos wire (cheap) or ceramic coating (expensive). 

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Spark Plugs:Performance plugs are pointless on a stock / marginally modified car. Iridium plugs have hardly any benefits and you will never notice them anyway. In case you do install the same, ensure that you pick up plugs with the correct heat range for your engine.

Plug wires:Same as above. After-market wires don’t add any performance to a stock or marginally modified engine. Only if your eventual modifications require an upgrade to a custom engine management system (or a high-performance ignition system) will your plug wires have some benefit. But at this stage, don’t opt for plug wires as you will only waste your money. Performance brake systems:By the time you reach stage three, chances are that your current braking power is ineffective toward handling the additional engine punch. Upgraded boosters, performance discs and street / performance brake pads are available to improve your cars stopping power.

Esteem VXi BS-III Technical Specs

Dimensions and Weights

Overall Length (mm) 4095

Overall Width (mm) 1575

Overall Height (mm) 1395

Wheel Base (mm) 2365

Ground Clearance (mm) 170

Front Track (mm) 1365

Rear Track (mm) 1340

Boot Space (liter) 376

Kerb Weight (kg) 875

Gross Vehicle Weight (kg) 1315

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Engine

Engine Type/Model 4 stroke, Water-cooled with 32-Bit Electronic Control Module (ECM)

Displacement cc 1298

Power (PS@rpm) 85PS @6000rpm

Torque (Nm@rpm) 110Nm @4500rpm

Valve Mechanism SOHC

Bore (mm) 74

Stroke (mm) 75.5

Compression Ratio 9:1

No of Cylinders (cylinder) 4

Cylinder Configuration In-line

Valves per Cylinder (value) 4

Fuel Type Petrol

Wheels and Tyres

Wheel Type

Wheel Size 13 Inch

Tyres 175/70 R 13

Brakes

Front Brakes Booster assisted ventilated disc

Rear Brakes Booster assisted drum

SOHC (Single Overhead Camshaft) Valve Mechanism

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In the regular four-stroke automobile engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the timing, lift and duration of each valve. Timing refers to when a valve is opened or closed with respect to the combustion cycle. Lift refers to how much the valve is opened. Duration refers to how long the valve is kept open. Due to the behavior of the gases (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high RPM. Optimal low RPM valve timing, lift and duration settings would result in insufficient fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM valve timing, lift and duration settings would result in very rough low RPM operation and difficult idling. The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough & stay open just the right amount of time for the engine speed in use. 

In practice, a fully variable valve timing engine is difficult to design and implement. Attempts have been made, using solenoids to control valves instead of the typical springs-and-cams setup, however these designs have not made it into production automobiles as they are very complicated and costly. 

The opposite approach to variable timing is to produce a camshaft which is better suited to high RPM operation. This approach means that the vehicle will run very poorly at low rpm (where most automobiles spend much of their time) and much better at high RPM. VTEC is the result of an effort to marry high RPM performance with low RPM stability.Additionally, Japan has a tax on engine displacement, requiring Japanese auto manufacturers to make higher-performing engines with lower displacement. In cars such as the Supra and 300ZX, this was accomplished with a turbocharger. In the case of the RX-7, a wankel rotary engine was used. VTEC serves as yet another method to derive very high specific output from lower displacement motors.

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DOHC (Double Overhead Camshaft)

Honda's VTEC system is a simple method of endowing the engine with multiple camshaft profiles optimized for low and high RPM operations.

Instead of one cam lobe actuating each valve, there are two - one optimized for low RPM stability & fuel efficiency, with the other designed

to maximize high RPM power output. Switching between the two cam lobes is determined by engine oil pressure, engine temperature, vehicle

speed, and engine speed. As engine RPM increases, a locking pin is pushed by oil pressure to bind the high RPM cam follower for operation. From this point on, the valve opens and closes according to the high-

speed profile, which opens the valve further and for a longer time. The DOHC VTEC system has high and low RPM cam lobe profiles on both the

intake and exhaust valve camshafts.

The VTEC system was originally introduced as a DOHC system in the 1989 Honda Integra sold in Japan, which used a 160 hp (119 kW) variant of the B16A engine. The US market saw the first VTEC system with the

introduction of the 1990 Acura NSX, which used a DOHC VTEC V6. DOHC VTEC motors soon appeared in other vehicles, such as the 1992 Acura

Integra GS-R. 

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SOHC VTEC 

As popularity and marketing value of the VTEC system grew, Honda applied the system to SOHC engines, which shares a common camshaft for both intake and exhaust valves. The trade-off is that SOHC engines

only benefit from the VTEC mechanism on the intake valves. This is because in the SOHC engine, the spark plugs need to be inserted at an

angle to clear the camshaft, and in the SOHC motor, the spark plug tubes are situated between the two exhaust valves, making VTEC on the

exhaust impossible.

SOHC

Honda's next version of VTEC, VTEC-E, was used in a slightly different way; instead of optimising performance at high RPMs, it was used to increase efficiency at low RPMs. At low RPMs, only one of the two intake valves is allowed to open, increasing the fuel/air atomization in the cylinder and thus allowing a leaner mixture to be used. As the engine's speed increases, both valves are needed to supply sufficient mixture. A sliding pin, as in the regular VTEC, is used to connect both valves together and allows opening of the second valve. 

3-Stage VTEC 

Honda also introduced a 3-stage VTEC system in select markets, which combines the features of both SOHC VTEC and SOHC VTEC-E. At low speeds, only one intake valve is used. At medium speeds, two are used. At high speeds, the engine switches to a high-speed cam profile as in regular VTEC. Thus, both low-speed economy and high-speed efficiency and power are improved.

Three-stage VTEC is a multi-stage implementation of VTEC and VTEC-E (colloquially known as dual VTEC), implemented in some 1995–present D series engines, allowing the engine to achieve both fuel efficiency and

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power. VTEC-E (for "Economy") is a form of VTEC that closes off one intake valve at low RPMs to give good economy at low power levels, while "VTEC" is a mode that allows for greater power at high RPMs, while giving relatively efficient performance at "normal" operating speeds. "Three-stage VTEC" gives both types in one engine, at the cost of greater complexity and expense.

Stage 1 – VTEC-EVTEC-E (economy) was designed to achieve better fuel economy, at the cost of performance. The engine operates in "12-valve mode", where one intake valve per cylinder in the 16-valve engine remains mostly closed to attain lean burn. The lean burn mode gets the air to fuel ratio above the 14.7:1 stoichiometric ratio and thus enables extra fuel saving. This works similarly to the principle which gave the Buick "Nailhead" V8 its reputation for high torque (in that case, the engine had notably small intake valves, giving good torque, but limiting peak power). In an engine running at lower RPMs, a smaller intake valve area forces a given volume of air to flow into the chamber faster; this causes the fuel to atomize better, and therefore burn far more efficiently. An average of 30 km/l (70.6 mpg-US) can be achieved while in lean burn at a constant speed of 60 km/h (37 mph).

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Stage 3 – VTECFrom ~5200 RPM to the rev limiter, the engine's high-lift VTEC cam lobe is engaged. A higher lift lowers restriction even more, giving the highest airflow. If one built a non-VTEC engine to make the maximum power, the trade-off would be very low efficiency at low RPMs in order to get the most flow possible at high RPMs. A three-stage allows the engine to run in "economy", "standard", and "high power" modes, while a VTEC only gives "standard" and "high power", and a VTEC-E only gives "economy" and "standard".The intake valves that were previously locked to the primary lobe are now locked to the mid lobe which opens earlier, stays open longer, opens higher, and has more overlap with the exhaust valve. This increases air flow in the high load/RPMs and broadening the power band even further.

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i-VTEC 

i-VTEC introduced continuously variable camshaft phasing on the intake cam of DOHC VTEC engines. The technology first appeared on Honda's K-series four cylinder engine family in 2001 (2002 in the U.S.). Valve lift and duration are still limited to distinct low and high rpm profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to maximum advance at full throttle and low rpms. The effect is further optimization of torque output, especially at low and midrange RPMs. 

In 2004, Honda introduced an i-VTEC V6 (an update of the venerable J-series), but in this case, i-VTEC had nothing to do with cam phasing. Instead, i-VTEC referred to Honda's cylinder deactivation technology which closes the valves on one bank of (3) cylinders during light load and low speed (below 80 mph) operation. The technology was originally introduced to the US on the Honda Odyssey Mini Van, and can now be

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found on the Honda Accord Hybrid and the 2006 Honda Pilot. An additional version of i-VTEC was introduced on the 2006 Honda Civic's R-series four cylinder engine. This implementation uses very small valve lifts at low rpm and light loads, in combination with large throttle openings (modulated by a drive-by-wire throttle system), to improve fuel economy by reducing pumping losses. 

With the continued introduction of vastly different i-VTEC systems, one may assume that the term is now a catch all for creative valve control technologies from Honda.

The SOHC design is inherently mechanically more efficient than a comparable pushrod design. This allows for higher engine speeds, which in turn will by definition increase power output for a given torque. The cams operate the valves directly or by a short rocker as opposed to overhead valve pushrod engines, which have tappets and long pushrods to transfer the movement of the lobes on the camshaft in the engine block to the valves in the cylinder head. 

SOHC designs offer reduced complexity compared to pushrod designs when used for multivalve heads, in which each cylinder has more than two valves. 

double overhead camshaft (also called double overhead cam, dual overhead cam or twincam) valvetrain layout is characterized by two camshafts being located within the cylinder head, where there are separate camshafts for inlet and exhaust valves. In engines with more than one cylinder bank (V engines) this designation means two camshafts per bank, for a total of four. 

Double overhead camshafts are not required in order to have multiple inlet or exhaust valves, but are necessary for more than 2 valves that are directly actuated (though still usually via tappets). Not all DOHC engines are multivalve engines — DOHC was common in two valve per cylinder heads for decades before multivalve heads appeared, however

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today DOHC is synonymous with multivalve heads, since almost all DOHC engines have between three and five valves per cylinder. 

BRAKING SYSTEM

Drum Brakes

A drum brake has a hollow drum that turns with the wheel. Its open back is covered by a stationary backplate on which there are two curved shoes carrying friction linings.The shoes are forced outwards by hydraulic pressure moving pistons in the brake's wheel cylinders, so pressing the linings against the inside of the drum to slow or stop it.Each brake shoe has a pivot at one end and a piston at the other. A leading shoe has the piston at the leading edge relative to the direction in which the drum turns.The rotation of the drum tends to pull the leading shoe firmly against it when it makes contact, improving the braking effect.Some drums have twin leading shoes, each with its own hydraulic cylinder; others have one leading and one trailing shoe - with the pivot at the front.This design allows the two shoes to be forced apart from each other by a single cylinder with a piston in each end.It is simpler but less powerful than the two-leading-shoe system, and is usually restricted to rear brakes.In either type, return springs pull the shoes back a short way when the brakes are released.Shoe travel is kept as short as possible by an adjuster. Older systems have manual adjusters that need to be turned from time to time as the friction linings wear. Later brakes have automatic adjustment by means of a ratchet.

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Components

Drum brake components include the backing plate, brake drum, shoe, wheel cylinder, and various springs and pins.Backing plateThe backing plate provides a base for the other components. It attaches to the axle sleeve and provides a non-rotating rigid mounting surface for the wheel cylinder, brake shoes, and assorted hardware. Since all braking operations exert pressure on the backing plate, it must be strong and wear-resistant. Levers for emergency or parking brakes, and automatic brake-shoe adjuster were also added in recent years.

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Back plate made in the pressing shop.Brake drumThe brake drum is generally made of a special type of cast iron that is heat-conductive and wear-resistant. It rotates with the wheel and axle. When a driver applies the brakes, the lining pushes radially against the inner surface of the drum, and the ensuing friction slows or stops rotation of the wheel and axle, and thus the vehicle. This friction generates substantial heat.Wheel cylinderOne wheel cylinder operates the brake on each wheel. Two pistons operate the shoes, one at each end of the wheel cylinder. Hydraulic pressure from the master cylinder acts on the piston cup, pushing the pistons toward the shoes, forcing them against the drum. When the driver releases the brakes, the brake shoe springs restore the shoes to their original (disengaged) position. The parts of the wheel cylinder are shown to the right.

Cut-away section of a wheel cylinder.Brake shoeBrake shoes are typically made of two pieces of sheet steel welded together. The friction material is either riveted to the lining table or attached with adhesive. The crescent-shaped piece is called the Web and contains holes and slots in different shapes for return springs,

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hold-down hardware, parking brake linkage and self-adjusting components. All the application force of the wheel cylinder is applied through the web to the lining table and brake lining. The edge of the lining table generally has three “V"-shaped notches or tabs on each side called nibs. The nibs rest against the support pads of the backing plate to which the shoes are installed. Each brake assembly has two shoes, a primary and secondary. The primary shoe is located toward the front of the vehicle and has the lining positioned differently than the secondary shoe. Quite often the two shoes are interchangeable, so close inspection for any variation is important.

Disc Brakes

A disc brake has a disc that turns with the wheel. The disc is straddled by a caliper, in which there are small hydraulic pistons worked by pressure from the master cylinder.The pistons press on friction pads that clamp against the disc from each side to slow or stop it. The pads are shaped to cover a broad sector of the disc.There may be more than a single pair of pistons, especially in dual-circuit brakes.The pistons move only a tiny distance to apply the brakes, and the pads barely clear the disc when the brakes are released. They have no return springs.Rubber sealing rings round the pistons are designed to let the pistons slip forward gradually as the pads wear down, so that the tiny gap remains constant and the brakes do not need adjustment.Many later cars have wear sensors leads embedded in the pads. When the pads are nearly worn out, the leads are exposed and short-circuited by the metal disc, illuminating a warning light on the instrument panel.

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A disc brake is a wheel brake which slows rotation of the wheel by the friction caused by pushing brake pads against a brake disc with a set of calipers. The brake disc (or rotor in American English) is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or the axle. To stop the wheel, friction material in the form of brake pads, mounted on a device called a brake caliper, is forced mechanically, hydraulically, pneumatically orelectromagnetically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop. Brakes convert motion to heat, and if the brakes get too hot, they become less effective, a phenomenon known as brake fade.

Disc-style brakes development and use began in England in the 1890s. The first caliper-type automobile disc brake was patented byFrederick William Lanchester in his Birmingham, UK factory in 1902 and used successfully on Lanchester cars. Compared to drum brakes, disc brakes offer better stopping performance, because the disc is more readily cooled. As a consequence discs are less prone to brake fade; and disc brakes recover more quickly from immersion (wet brakes are less effective). Most drum brake designs have at least one leading shoe, which gives a servo-effect. By contrast, a disc brake has no self-

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servo effect and its braking force is always proportional to the pressure placed on the brake pad by the braking system via any brake servo, braking pedal or lever. This tends to give the driver better "feel" to avoid impending lockup. Drums are also prone to "bell mouthing", and trap worn lining material within the assembly, both causes of various braking problems.

The brake disc is the disc component of a disc brake against which the brake pads are applied. The material is typically grey iron,[14] a form of cast iron. The design of the disc varies somewhat. Some are simply solid, but others are hollowed out with fins or vanes joining together the disc's two contact surfaces (usually included as part of a casting process). The weight and power of the vehicle determines the need for ventilated discs.[10] The "ventilated" disc design helps to dissipate the generated heat and is commonly used on the more-heavily-loaded front discs.Many higher-performance brakes have holes drilled through them. This is known as cross-drilling and was originally done in the 1960s on racing cars. For heat dissipation purposes, cross drilling is still used on some braking components, but is not favored for racing or other hard use as the holes are a source of stress cracks under severe conditions.Discs may also be slotted, where shallow channels are machined into the disc to aid in removing dust and gas. Slotting is the preferred method in most racing environments to remove gas and water and to deglaze brake pads. Some discs are both drilled and slotted. Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids vitrification of their surfaces.As a way of avoiding thermal stress, cracking and warping, the disc is sometimes mounted in a half loose way to the hub with coarse splines. This allows the disc to expand in a controlled symmetrical way and with less unwanted heat transfer to the hub.On the road, drilled or slotted discs still have a positive effect in wet conditions because the holes or slots prevent a film of water building up between the disc and the pads. Cross-drilled discs may eventually crack at the holes due to metal fatigue. Cross-drilled brakes that are manufactured poorly or subjected to high stresses will crack much sooner and more severely.

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Run-outRun-out is measured using a dial indicator on a fixed rigid base, with the tip perpendicular to the brake disc's face. It is typically measured about 1⁄2 in (12.7 mm) from the outside diameter of the disc. The disc is spun. The difference between minimum and maximum value on the dial is called lateral run-out. Typical hub/disc assembly run-out specifications for passenger vehicles are around 0.0020 in (50.8 µm). Runout can be caused either by deformation of the disc itself or by runout in the underlying wheel hub face or by contamination between the disc surface and the underlying hub mounting surface. Determining the root cause of the indicator displacement (lateral runout) requires disassembly of the disc from the hub. Disc face runout due to hub face runout or contamination will typically have a period of 1 minimum and 1 maximum per revolution of the brake disc.Discs can be machined to eliminate thickness variation and lateral run-out. Machining can be done in situ (on-car) or off-car (bench lathe). Both methods will eliminate thickness variation. Machining on-car with proper equipment can also eliminate lateral run-out due to hub-face non-perpendicularity.Incorrect fitting can distort (warp) discs; the disc's retaining bolts (or the wheel/lug nuts, if the disc is simply sandwiched in place by the wheel, as on many cars) must be tightened progressively and evenly. The use of air tools to fasten lug nuts is extremely bad practice, unless a torque tube is also used. The vehicle manual will indicate the proper pattern for tightening as well as a torque rating for the bolts. Lug nuts should never be tightened in a circle. Some vehicles are sensitive to the force the bolts apply and tightening should be done with a torque wrench.Often uneven pad transfer is confused for disc warping. In reality, the majority of brake discs which are diagnosed as "warped" are actually simply the product of uneven transfer of pad material. Uneven pad transfer will often lead to a thickness variation of the disc. When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightly; this is pedal pulsation. The thickness variation can be felt by the driver when it is approximately 0.17 mm (0.0067 in) or greater (on automobile discs).This type of thickness variation has many causes, but there are three primary mechanisms which contribute the most to the propagation of disc thickness variations connected to uneven pad transfer. The first is improper selection of brake pads for a given application. Pads which are effective at low temperatures, such as when braking for the first

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time in cold weather, often are made of materials which decompose unevenly at higher temperatures. This uneven decomposition results in uneven deposition of material onto the brake disc. Another cause of uneven material transfer is improper break in of a pad/disc combination. For proper break in, the disc surface should be refreshed (either by machining the contact surface or by replacing the disc as a whole) every time the pads are changed on a vehicle. Once this is done, the brakes are heavily applied multiple times in succession. This creates a smooth, even interface between the pad and the disc. When this is not done properly the brake pads will see an uneven distribution of stress and heat, resulting in an uneven, seemingly random, deposition of pad material. The third primary mechanism of uneven pad material transfer is known as "pad imprinting." This occurs when the brake pads are heated to the point that the material begins to break-down and transfer to the disc. In a properly broken in brake system (with properly selected pads), this transfer is natural and actually is a major contributor to the braking force generated by the brake pads. However, if the vehicle comes to a stop and the driver continues to apply the brakes, the pads will deposit a layer of material in the shape of the brake pad. This small thickness variation can begin the cycle of uneven pad transfer.

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IN-LINE CYLINDER CONFIGURATION

The inline-four engine or straight-four engine is a type of internal combustion four cylinder engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all thepistons driving a common crankshaft. Where it is inclined, it is sometimes called a slant-four. In a specification chart or when an abbreviation is used, an inline-four engine is listed either as I4 or L4 (for longitudinal, to avoid confusion between the digit 1 and the letter I).The inline-four layout is in perfect primary balance and confers a degree of mechanical simplicity which makes it popular for economy cars. However, despite its simplicity, it suffers from a secondary imbalance which causes minor vibrations in smaller engines. These vibrations become more powerful as engine size and power increase, so the more powerful engines used in larger cars generally are more complex designs with more than four cylinders.Today almost all manufacturers of four-cylinder engines for automobiles produce the inline-four layout, with Subaru's flat-four engine being a notable exception, and so four-cylinder is synonymous with and a more widely used term than inline-four. The inline-four is the most common engine configuration in modern cars, while the V6 engine is the second most popular. In the late 2000s, with auto manufacturers making efforts to reduce emissions; and increase fuel efficiency due to the high price of oil and the economic recession, the proportion of new vehicles sold in the U.S. with four-cylinder engines (largely of the inline-four type) rose from 30 percent to 47 percent between 2005 and 2008, particularly in mid-size vehicles where a decreasing number of buyers have chosen the V6 performance option.This inline engine configuration is the most common in cars with a displacement up to 2.4 L. The usual "practical" limit of the displacement of inline-four engines in a car is around 2.7 L. However, Porsche used a 3.0 L four in its 944 S2 and 968 sports cars,

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the International Harvester Scout was available with a 3.2 L inline four from 1965 until 1980 and Rolls-Royce produced several inline-four engines of 2,838 cc with basic cylinder dimensions of 3.5 in (89 mm) diameter and 4.5 in (110 mm) stroke (Rolls-Royce B40). Early vehicles also tended to have engines with larger displacements to develop horsepower and torque. The Model A Ford was built with a 3.3 L inline-four engine.Inline-four diesel engines, which are lower revving than gasoline engines, often exceed 3.0 L. Mitsubishi still employs a 3.2 L inline-four turbodiesel in its Pajero (called the Shogun or Montero in certain markets), and Tata Motors employs a 3.0 L inline-four diesel in its Spacio and Sumo Victa.The Toyota B engine series of diesel engines varies in displacement from 3.0- 4.1 L. The largest engine in that series was used in the Mega Cruiser.One of the strongest Powerboat-4-cylinders is the Volvo Penta D4-300 turbodiesel. This is a 3.7 L-inline-4 with 300 hp (224 kW) and 516 lb·ft (700 N·m) .One of the strongest inline-4-engines is the MAN D0834 engine. This is a 4.6 L inline-4 with 220 hp (164 kW) and 627 lb·ft (850 N·m), which is available for the MAN TGL light-duty truck and VARIOmobil motorhomes.The Isuzu Forward is a medium-duty truck which is available with a 5.2 L inline-four engine that delivers 210 hp (157 kW) and 470 lb·ft (640 N·m) .The Hino Ranger is a medium-duty truck which is available with a 5.1 L inline-four engine that delivers 175 hp (130 kW) and 465 lb·ft (630 N·m) . The earlier Hino Ranger even had a 5.3 L inline-four engine.The Kubota M135X is a tractor with a 6.1 L inline-four. This turbo-diesel engine has a bore of 118 mm (4.6 in) and a relative long stroke of 140 mm (5.5 in).Larger inline-four engines are used in industrial applications, such as in small trucks and tractors, are often found with displacements up to about 4.6 L. Diesel engines for stationary, marine and locomotive use (which run at low speeds) are made in much larger sizes.Brunswick Marine built a 127 kW (170 bhp) 3.7 L 4-cylinder gasoline engine (designated as the "470") for their Mercruiser Inboard/outboard line. The block was formed from one half of a Ford 460 cubic inch V8 engine. This engine was produced in the 1970s and 1980s.

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One of the largest inline-four engines is the MAN B&W 4K90 marine engine. This two-stroke turbo-diesel has a giant displacement of 6,489 L. This results from a massive 0.9 meter bore and 2.5 meter stroke. The 4K90 engine develops 18,280 kW (24,854 PS; 24,514 hp) at 94 rpm and weighs 787 tons.Displacement can also be very small, as found in kei cars sold in Japan, such as the Subaru EN series; engines that started out at 550 cc and are currently at 660 cc, with variable valve timing, DOHC and superchargers resulting in engines that often claim the legal maximum of 64 PS (47 kW; 63 bhp).

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Piston speedAn even-firing inline-four engine is in primary balance because the pistons are moving in pairs, and one pair of pistons is always moving up at the same time as the other pair is moving down. However, piston acceleration and deceleration are greater in the top half of the crankshaft rotation than in the bottom half, because the connecting rods are not infinitely long, resulting in a non-sinusoidal motion. As a result, two pistons are always accelerating faster in one direction, while the other two are accelerating more slowly in the other direction, which leads to a secondary dynamic imbalance that causes an up-and-down vibration at twice crankshaft speed. This imbalance is common among all piston engines, but the effect is particularly strong on inline-four because of the two pistons always moving together.The reason for the piston's higher speed during the 180° rotation from mid-stroke through top-dead-centre, and back to mid-stroke, is that the minor contribution to the piston's up/down movement from the connecting rod's change of angle here has the same direction as the major contribution to the piston's up/down movement from the up/down movement of the crank pin. By contrast, during the 180° rotation from mid-stroke through bottom-dead-centre and back to mid-stroke, the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the opposite direction of the major contribution to the piston's up/down movement from the up/down movement of the crank pin.The strength of this imbalance is determined by 1. Reciprocating mass, 2. Ratio of connecting rod length to stroke, and 3. Acceleration of piston movement. So small displacement engines with light pistons show little effect, and racing engines use long connecting rods. However, the effect grows exponentially with crankshaft rotational speed. See crossplanearticle for unusual inline-four configurations.Balance shaft useMost inline-four engines below 2.0 L in displacement rely on the damping effect of their engine mounts to reduce the vibrations to acceptable levels. Above 2.0 L, most modern inline-four engines now use balance shafts to eliminate the secondary vibrations. In a system invented by Dr. Frederick W. Lanchester in 1911, an inline-four engine uses two balance shafts, rotating in opposite directions at twice the crankshaft's speed, to offset the differences in piston speed.[12] In the 1970s, Mitsubishi Motors patented these balancer shafts to be located at different heights to further counter the rotational vibration created by the left and right swinging motion of connecting rods. Porsche, who used this technology on Porsche 944, and other car makers bought the license to this patent.

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However, in the past, there were numerous examples of larger inline-fours without balance shafts, such as the Citroën DS 23 2,347 cc engine that was a derivative of the Traction Avantengine, the 1948 Austin 2,660 cc engine used in the Austin-Healey 100 and Austin Atlantic, the 3.3 L flathead engine used in the Ford Model A (1927), and the 2.5 L GM Iron Duke engine used in a number of American cars and trucks. Soviet/Russian GAZ Volga cars and UAZ SUVs, vans and light trucks used aluminium big-bore inline-four engines (2.5 or later 2.9 L) with no balance shafts from the 1950s-1990s. These engines were generally the result of a long incremental evolution process and their power was kept low compared to their capacity. However, the forces increase with the square of the engine speed — that is, doubling the speed makes the vibration four times more forceful — so some modern high-speed inline-fours, generally those with a displacement greater than 2.0 litres, have more need to use balance shafts to offset the vibration.

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ELECTRONIC CONTROL MODULE (ECM)

In automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical system or subsystems in a motor vehicle.Types of ECU include electronic/engine control module (ECM), powertrain control module (PCM), transmission control module (TCM), brake control module (BCM or EBCM), central control module (CCM), central timing module (CTM), general electronic module (GEM), body control module (BCM), suspension control module (SCM), control unit, or control module. Taken together, these systems are sometimes referred to as the car's computer. (Technically there is no single computer but multiple ones.) Sometimes one assembly incorporates several of the individual control modules (PCM is often both engine and transmission)[1]

Some modern motor vehicles have up to 80 ECUs. Embedded software in ECUs continue to increase in line count, complexity, and sophistication.[2] Managing the increasing complexity and number of ECUs in a vehicle has become a key challenge for original equipment manufacturers (OEMs).

An engine control unit (ECU), most commonly called the powertrain control module (PCM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps (called lookup tables), and adjusting the engine actuators accordingly.Before ECUs, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical andpneumatic means. One of the earliest attempts to

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use such a unitized and automated device to manage multiple engine control functions simultaneously was the "Kommandogerät" created by BMW in 1939, for their 801 14-cylinder aviation radial engine.[citation

needed] This device replaced the 6 controls used to initiate hard acceleration with one control in the 801 series-equipped aircraft. However, it had some problems: it would surge the engine, making close formation flying of the Fw 190 somewhat difficult, and at first it switched supercharger gears harshly and at random, which could throw the aircraft into an extremely dangerous stall or spin.

Working of ECU

Control of Air/Fuel ratioFor an engine with fuel injection, an engine control unit (ECU) will determine the quantity of fuel to inject based on a number of parameters. If the throttle position sensor is showing the throttle pedal is pressed further down, the mass flow sensor will measure the amount of additional air being sucked into the engine and the ECU will inject fixed quantity of fuel into the engine ( most of the engine fuel inlet quantity is fixed). If the engine coolant temperature sensor is showing the engine has not warmed up yet, more fuel will be injected (causing the engine to run slightly 'rich' until the engine warms up). Mixture control on computer controlled carburetors works similarly but with a mixture control solenoid or stepper motor incorporated in the float bowl of the carburetor.Control of ignition timingA spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy. If the ECU detects knock, a condition which is potentially destructive to engines, and determines it to be the result of the ignition timing occurring too early in the compression stroke, it will delay (retard) the timing of the spark to prevent this. Since knock tends to occur more easily at lower rpm, the ECU may send a signal for the automatic transmission to downshift as a first attempt to alleviate knock.Control of idle speedMost engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. Early carburetor-based systems used a programmable throttle stop using a

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bidirectional DC motor. Early TBI systems used an idle air control stepper motor. Effective idle speed control must anticipate the engine load at idle. Changes in this idle load may come from HVAC systems, power steering systems, power brake systems, and electrical charging and supply systems. Engine temperature and transmission status, and lift and duration of camshaft also may change the engine load and/or the idle speed value desired.A full authority throttle control system may be used to control idle speed, provide cruise control functions and top speed limitation.Control of variable valve timingSome engines have Variable Valve Timing. In such an engine, the ECU controls the time in the engine cycle at which the valves open. The valves are usually opened sooner at higher speed than at lower speed. This can optimize the flow of air into the cylinder, increasing power and the economy.

Electronic valve controlExperimental engines have been made and tested that have no camshaft, but have full electronic control of the intake and exhaust valve opening, valve closing and area of the valve opening. Such engines can be started and run without a starter motor for certain multi-cylinder engines equipped with precision timed electronic ignition and fuel injection. Such astatic-start engine would provide the efficiency and pollution-reduction improvements of a mild hybrid-electric drive, but without the expense and complexity of an oversized starter motor.The first production engine of this type was invented ( in 2002) and introduced (in 2009) by Italian automaker Fiat in the Alfa Romeo MiTo. Their Multiair engines use electronic valve control which drastically improve torque and horsepower, while reducing fuel consumption as much as 15%. Basically, the valves are opened by hydraulic pumps, which are operated by the ECU. The valves can open several times per intake stroke, based on engine load. The ECU then decides how much fuel should be injected to optimize combustion.For instance, when driving at a steady speed, the valve will open and a bit of fuel will be injected, the valve then closes. But, when you suddenly stamp on the throttle, the valve will open again in that same intake stroke and much more fuel will be injected so that you start to accelerate immediately. The ECU then calculates engine load at that exact RPM and decides how to open the valve: early, or late, wide open, or just half open. The optimal opening and timing are always

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reached and combustion is as precise as possible. This, of course, is impossible with a normal camshaft, which opens the valve for the whole intake period, and always to full lift.And not to be overlooked, the elimination of cams, lifters, rockers, and timing set not only reduces weight and bulk, but also friction. A significant portion of the power that an engine actually produces is used up just driving the valve train, compressing all those valve springs thousands of times a minute.Once more fully developed, electronic valve operation will yield even more benefits. Cylinder deactivation, for instance, could be made much more fuel efficient if the intake valve could be opened on every downstroke and the exhaust valve opened on every upstroke of the deactivated cylinder or "dead hole". Another even more significant advancement will be the elimination of the convention throttle. When a car is run at part throttle, this interruption in the airflow causes excess vacuum, which causes the engine to use up valuable energy acting as a vacuum pump. BMW attempted to get around this on their V-10 powered M5, which had individual throttle butterflies for each cylinder, placed just before the intake valves. With electronic valve operation, it will be possible to control engine speed by regulating valve lift. At part throttle, when less air and gas are needed, the valve lift would not be as great. Full throttle is achieved when the gas pedal is depressed, sending an electronic signal to the ECU, which in turn regulates the lift of each valve event, and opens it all the way up.

Programmable ECUs

A special category of ECUs are those which are programmable. These units do not have a fixed behaviour and can be reprogrammed by the user.Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger, adding or changing of an intercooler, changing of the exhaust system or a conversion to run on alternative fuel. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop connected using a serial or USB cable, while the engine is running.The programmable ECU may control the amount of fuel to be injected into each cylinder. This varies depending on the engine's RPM

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and the position of the accelerator pedal (or themanifold air pressure). The engine tuner can adjust this by bringing up a spreadsheet-like page on the laptop where each cell represents an intersection between a specific RPM value and an accelerator pedal position (or the throttle position, as it is called). In this cell a number corresponding to the amount of fuel to be injected is entered. This spreadsheet is often referred to as a fuel table or fuel map.By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.Other parameters that are often mappable are:

Ignition Timing: Defines at what point in the engine cycle the spark plug should fire for each cylinder. Modern systems allow for individual trim on each cylinder for per-cylinder optimization of the ignition timing.

Rev. limit: Defines the maximum RPM that the engine is allowed to reach. After this fuel and/or ignition is cut. Some vehicles have a "soft" cut-off before the "hard" cut-off. This "soft cut" generally functions by retarding ignition timing to reduce power output and thereby slow the acceleration rate just before the "hard cut" is hit.

Water temperature correction: Allows for additional fuel to be added when the engine is cold, such as in a winter cold-start scenario or when the engine is dangerously hot, to allow for additional cylinder cooling (though not in a very efficient manner, as an emergency only).

Transient fueling: Tells the ECU to add a specific amount of fuel when throttle is applied. The is referred to as "acceleration enrichment".

Low fuel pressure modifier: Tells the ECU to increase the injector fire time to compensate for an increase or loss of fuel pressure.

Closed loop lambda: Lets the ECU monitor a permanently installed lambda probe and modify the fueling to achieve the targeted air/fuel ratio desired. This is often the stoichiometric (ideal) air fuel ratio, which on traditional petrol (gasoline) powered vehicles this air:fuel ratio is 14.7:1. This can also be a much richer ratio for when the engine is under high load, or

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possibly a leaner ratio for when the engine is operating under low load cruise conditions for maximum fuel efficiency.

A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviors during a race by downloading the log data and looking for anomalies after the event. The data logger usually has a capacity between 0.5 and 16 megabytes.

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AIR INTAKE SYSTEMThere are a handful of car owners out there that are not quite sure what an air intake system does, how it works or how important it is to a car. In the 1980s, the first air intake systems were offered and consisted of moulded plastic intake tubes and a cone-shaped cotton gauze air filter. A decade later, overseas manufacturers began importing popular Japanese air intake system designs for the sport compact market. Now, with the technological advancement and ingenious engineering minds, intake systems are available in metal tube designs, allowing a greater degree of customisation. The tubes are typically powder-coated or painted to match a vehicle.

The function of the air intake system is to allow air to reach your car engine. Oxygen in the air is one of the necessary ingredients for the engine combustion process. A good air intake system allows for clean and continuous air into the engine, thereby achieving more power and better mileage for your car.

A modern automobile air intake system has three main parts: air filter, mass flow sensor and throttle body. Located directly behind the front grille, the air intake system draws air through a long plastic tube going into the air filter housing, which will be mixed with the car fuel. Only then will the air be sent to the intake manifold that supplies the fuel/air mixture to the engine cylinders.

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Air Filter

An air filter is an important part of a car's intake system, because it is through the air filter that the engine "breathes". It is usually a plastic or metal box in which the air filter sits.

An engine requires an exact mixture of fuel and air in order to run, and all of the air enters the system first through the air filter. The air filter's job is to filter out dirt and other foreign particles in the air, preventing them from entering the system and possibly damaging the engine.

The air filter is usually located in the air stream to your throttle valve assembly and intake manifold. It is found in a compartment in an air duct to the throttle valve assembly under the hood of your car.

Open pods are generally larger in size and requires the removal of your whole standard air intake unit. They have the best performance when it comes to air intake, but lacks in filtration capabilities.

Drop in air filters on the other hand provide ‘plug and play’ bliss for beginners, as you can simply swap your OEM air filter for these things. No modifications necessary. Air intake is generally better than standard OEM air filters, but again, filtration is not as good.

Deciding on which to get for your car is simple. It all depends on the type of transmission your car uses. An automatic car will benefit from a drop in filter, but will have little or no improvements if fitted with an open pod; the reason being open pods require a rev above 3,000 rpm to be able to perform optimally, and automatic cars generally change gears before the 3,000 rpm mark.

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Manual transmission cars however can benefit from both open pod and drop in filters, as the engine revs easier and the driver can decide when to change gears.

cold air is heavier than hot air, so theoretically in the atmosphere, cold air should be located closer to the ground. With this in mind, imagine if you place your air intake hose (hose that directs air into the air filter unit) at the front of the car, and at a low position, cold, or in the case of South East Asia, air that is not so warm, can get into the combustion chamber and help the combustion even more, thus allowing better acceleration.

This however requires one to drill a hole in the middle of one’s bumper. I have seen some pretty well done CAI, but for the most of it, it will look like your car just had a molar removed.

A simple test to see how dirty your air filter is and also to determine its filtration capabilities is to simply put it up against a source of light. A clean filter would allow one to see light poking through the ‘pores’ of the filter whereas a dirty filter would block out the light entirely. Air filters with good filtration capabilities usually get dirty faster, meaning that it’s doing a good job at filtration, whilst a filter with less filtration capabilities would stay cleaner longer.

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A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mould, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds or ozone. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.

Some buildings, as well as aircraft and other man-made environments (e.g., satellites and space shuttles) use foam, pleated paper, or spun fiber glass filter elements. Another method, air ionisers, use fibers or elements with a static electric charge, which attract dust particles. The air intakes of internal combustion engines and compressors tend to use either paper, foam, or cotton filters. Oil bath filters have fallen out of favour. The technology of air intake filters of gas turbines has improved significantly in recent years, due to improvements in the aerodynamics and fluid-dynamics of the air-compressor part of the Gas Turbines.

Mass flow sensor

A mass air flow sensor is used to find out the mass of air entering a fuel-injected internal combustion engine. From mass flow sensor, then, does it goes to the throttle body.

There are two common types of mass airflow sensors in use on automotive engines. They are the vane meter and the hot wire.

The vane type has a flap that is pushed by the incoming air. The more air coming in, the more the flap is pushed backed. There is also a second vane behind the main one that fits into a closed camber that

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dampens the movement of the vane giving a more accurate measurement.

The hot wire uses a series of wires strung in the air stream. The electrical resistance of the wire increases as the wire's temperature increases, which limits electrical current flowing through the circuit.

When air flows past the wire, it cools, decreasing its resistance, which in turn allows more current to flow through the circuit. However, as

more current flows, the wire's temperature increases until the

resistance reaches equilibrium

The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flowsensors for determining the quantity of intake air in each piston stroke.

Vane meter sensor (VAF sensor)

The VAF (volume air flow) sensor measures the air flow into the engine with a spring-loaded air flap/door attached to a variable resistor (potentiometer). The vane moves in proportion to the airflow. A voltage is applied to the potentiometer and a proportional voltage appears on the output terminal of the potentiometer in proportion to the distance the vane moves, or the movement of the vane may directly regulate the amount of fuel injected, as in the K-Jetronic system.Many VAF sensors have an air-fuel adjustment screw, which opens or closes a small air passage on the side of the VAF sensor. This screw controls the air-fuel mixture by letting a metered amount of air flow past the air flap, thereby, leaning or richening the mixture. By turning

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the screw clockwise the mixture is enriched and counterclockwise the mixture is leaned.The vane moves because of the drag force of the air flow against it; it does not measure volume or mass directly. The drag force depends on air density (air density in turn depends on air temperature), air velocity and the shape of the vane, see drag equation. Some VAF sensors include an additional intake air temperature sensor (IAT sensor) to allow the engines ECU to calculate the density of the air, and the fuel delivery accordingly.The vane meter approach has some drawbacks:

it restricts airflow which limits engine output its moving electrical or mechanical contacts can wear finding a suitable mounting location within a confined engine

compartment is problematic the vane has to be oriented with respect to gravity. in some manufacturers fuel pump control was also part on the

VAF internal wiring.

Hot wire sensor (MAF)

A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. The theory of operation of the hot wire mass airflow sensor is similar to that of thehot wire anemometer (which determines air velocity). This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire. The wire's electrical resistance increases as the wire’s temperature increases, which varies the electrical current flowing through, or the voltage over the circuit, according to Ohm's law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit or causing a smaller voltage drop over the wire. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current or voltage drop is proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement into a calibrated signal which is sent to the ECU.If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike the vane

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meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume. (See stoichiometry.)This sensor sometimes employs a mixture screw, but this screw is fully electronic and uses a variable resistor (potentiometer) instead of an air bypass screw. The screw needs more turns to achieve the desired results. A hot wire burn-off cleaning circuit is employed on some of these sensors. A burn-off relay applies a high current through the platinum hot wire after the vehicle is turned off for a second or so, thereby burning or vaporizing any contaminants that have stuck to the platinum hot wire element.The hot film MAF sensor works somewhat similar to the hot wire MAF sensor, but instead it usually outputs a frequency signal. This sensor uses a hot film-grid instead of a hot wire. It is commonly found in late 80’s early 90’s fuel-injected vehicles. The output frequency is directly proportional to the air mass entering the engine. So as mass flow increases so does frequency. These sensors tend to cause intermittent problems due to internal electrical failures. The use of an oscilloscope is strongly recommended to check the output frequency of these sensors. Frequency distortion is also common when the sensor starts to fail. Many technicians in the field use a tap test with very conclusive results. Not all HFM systems output a frequency. In some cases, this sensor works by outputting a regular varying voltage signal.

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Throttle Body

The throttle body is the part of the air intake system that controls the amount of air flowing into an engine's combustion chamber. It consists of a bored housing that contains a throttle plate that rotates on a shaft. When the accelerator is depressed, the throttle plate opens and allows air into the engine. When the accelerator is released, the throttle plate closes and effectively chokes-off air flow into the combustion chamber. This process effectively controls the rate of combustion and ultimately the speed of the vehicle.

The throttle body is usually located between the air filter box and the intake manifold, and it is usually located near the mass airflow sensor.

the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main. The throttle body is usually located between the air filter box and the intake manifold, and it is usually attached to, or near, the mass airflow sensor.The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow.On many cars, the accelerator pedal motion is communicated via the throttle cable, to activate the throttle linkages, which move the throttle plate. In cars with electronic throttle control (also known as "drive-by-wire"), an electric motor controls the throttle linkages and the accelerator pedal connects not to the throttle body, but to a sensor, which sends the pedal position to the Engine Control Unit (ECU). The ECU determines the throttle opening based on accelerator pedal position and inputs from other engine sensors.

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Cold air intake and how it works

A cold air intake is used to bring cooler air into a car's engine, to increase engine power and efficiency. The most efficient intake systems utilise an air box which is sized to complement the engine and will extend the power band of the engine. The intake snorkel, or the

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opening for the intake air to enter the system, must be large enough to ensure sufficient air is available to the engine under all conditions from idle to full throttle.

Cold air intakes operate on the principle of increasing the amount of oxygen available for combustion with fuel. Because cooler air has a higher density (greater mass per unit volume), cold air intakes generally work by introducing cooler air from outside the hot engine bay.

The most basic cold air intake replaces the stock air box with a short metal or plastic tube leading to a conical air filter, called a short ram air intake. The power gained by this method can vary depending on how restrictive the factory air box is.

Well-designed intakes use heat shields to isolate the air filter from the rest of the engine compartment, providing cooler air from the front or side of the engine bay. Some systems called "fender mount" move the filter into the fender wall, this system draws air up through the fender wall which provides even more isolation and still cooler air.Some of the advantages of having a cold air intake include an increase in horsepower and torque. As a cold air intake draws in a higher volume of air which may be much cooler, your engine can breathe easier than with a limiting stock system. With your combustion chamber filled by cooler, oxygen-rich air, fuel burns at a more efficient mixture. You get more power and torque out of every drop of fuel when it's combined with the right amount of air.

Another advantage to having a cold air intake is improved throttle response and fuel economy in most cases. Stock intakes often deliver warmer, fuel-rich combustion mixtures that cause your engine to lose power and responsiveness while running hotter and more sluggishly. Cold air intakes can help your fuel economy by improving your air to fuel ratio.

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EXISTING EXHAUST SYSTEM IN DETAILAn exhaust system is usually piping used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one or more of:

Cylinder head and exhaust manifold A turbocharger to increase engine power. A catalytic converter to reduce air pollution. A muffler (North America) / silencer (Europe), to reduce noise.

TerminologyManifold or header

In most production engines, the manifold is an assembly designed to collect the exhaust gas from two or more cylinders into one pipe. Manifolds are often made of cast iron in stock production cars, and may have material-saving design features such as to use the least metal, to occupy the least space necessary, or have the lowest production cost. These design restrictions often result in a design that is cost effective but that does not do the most efficient job of venting the gases from the engine. Inefficiencies generally occur due to the nature of the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates a back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities. In Australia, the pipe of the exhaust system which attaches to the exhaust manifold is called the 'engine pipe' and the pipe emitting gases to ambient air called the 'tail pipe'.A header (sometimes called set of extractors in Australia) is a manifold specifically designed for performance.[1] During design, engineers create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to

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the common outlet all equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back towards other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolutions per minute range.Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective well-designed headers specifically for their car. Headers can also be custom designed by a custom shop. Due to the advanced materials that some aftermarket headers are made of, this can be expensive. Luckily, an exhaust system can be custom built for any car, and generally is not specific to the car's motor or design except for needing to properly connect solidly to the engine. This is usually accomplished by correct sizing in the design stage, and selecting a proper gasket type and size for the engine.

Header-backThe Header-back (or header back) is the part of the exhaust system from the outlet of the header to the final vent to open air — everything from the header back. Header-back systems are generally produced as aftermarket performance systems for cars without turbochargers.

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Turbo-backThe Turbo-back (or turbo back) is the part of the exhaust system from the outlet of a turbocharger to the final vent to open air. Turbo-back systems are generally produced as aftermarket performance systems for cars with turbochargers. Some turbo-back (and header-back) systems replace stock catalytic converters with others having less flow restriction.With or without catalytic converterSome systems (including in former time all systems) (sometimes nowadays called catless or de-cat) eliminate the catalytic converter. This is illegal in some places if the vehicle is driven on public roads.Cat-backCat-back (also cat back and catback) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This generally includes the pipe from the converter to the muffler, the muffler, and the final length of pipe to open air.Cat-back exhaust systems generally use larger diameter pipe than the stock system. Good systems will have mandrel-bent turns that allow the exhaust gases to exit with as little back pressure as possible. The mufflers included in these kits are often glass packs, to reduce back pressure. If the system is engineered more for show than functionality, it may be tuned to enhance the lower sounds that are lacking from high-RPM low-displacement engines.

Tailpipe and exhaustWith trucks, sometimes the silencer is crossways under the front of the cab and its tailpipe blows sideways to the offside (right side if driving on the left, left side if driving on the right). The side of a passenger car on which the exhaust exits beneath the rear bumper usually indicates the market for which the vehicle was designed, i.e. Japanese (and some older British) vehicles have exhausts on the right so they are furthest from the curb in countries which drive on the left, while European vehicles have exhausts on the left.The end of the final length of exhaust pipe where it vents to open air, generally the only visible part of the exhaust system part on a vehicle, often ends with just a straight or angled cut, but may include a fancy tip. The tip is sometimes chromed. It is often of larger pipe than the rest of the exhaust system. This produces a final reduction in pressure, and sometimes used to enhance the appearance of the car.

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In the late 1950s in the United States manufacturers had a fashion in car styling to form the rear bumper with a hole at each end through which the exhaust would pass. Two outlets symbolized V-8 power, and only the most expensive cars (Cadillac, Lincoln, Imperial, and Packard) were fitted with this design. One justification for this was that luxury cars in those days had such a long rear overhang that the exhaust pipe scraped the ground when the car traversed ramps. The fashion disappeared after customers noted that the rear end of the car, being a low-pressure area, collected soot from the exhaust and its acidic content ate into the chrome-plated rear bumper.When a bus, truck or tractor or excavator has a vertical exhaust pipe (called stacks or pipes behind the cab), sometimes the end is curved, or has a hinged cover flap which the gas flow blows out of the way, to try to prevent foreign objects (including droppings from a bird perching on the exhaust pipe when the vehicle is not being used) getting inside the exhaust pipe.In some trucks, when the silencer is front-to-back under the chassis, the end of the tailpipe turns 90° and blows downwards. That protects anyone near a stationary truck from getting a direct blast of the exhaust gas, but often raises dust when the truck is driving on a dry dusty unmade surface such as on a building site.Lake pipesLake pipes are a type of aftermarket performance exhaust added by performance enthusiasts. The exhaust is routed from the exhaust manifold and routed along or beside the bottom of the car body beneath the doors. They were usually chrome plated. Usually they also offered a performance boost as they had less back pressure than conventional exhaust, along with less environmental control (no catalytic converter).

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Though it might seem inefficient to have a ton of pipes instead of just one, really, all those segments serve a purpose. For one, bending pipes is hard work, and it's easier to connect small angled segments to straight pipes than it is to shape one long, expensive, heavy pipe to fit every contour of a car. Also, exhaust system components wear out at regular intervals (depending, of course, on the manufacturer, its materials, driving conditions and environmental factors). It's easier and less expensive to replace one rusted-out segment of pipe, banged-up muffler, or worn-out catalytic converter than it would be to install a whole new system.

The gaskets that are fitted between each pipe play a very important role. It's difficult, if not impossible, to form a flawless metal-to-metal seal, so gaskets are sandwiched between each connection to prevent the poisonous gases from escaping prematurely. They're made of fiber or other heavy-duty, heat resistant materials, which have just enough flexibility to compress slightly when the pipes are clamped tightly together. This helps form a tight seal.

The muffler is another key part of the exhaust system. It looks like a large round or oval chamber (usually, but not always, found near the back of the car). That chamber has a very complex design, though -- it's responsible for silencing most of the engine's noise, even though it has to allow the exhaust to continue flowing smoothly. A series of

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chambers and tubes, filled with rock, wool, or synthetic fibers, absorbs and controls the noise. And that's not all -- the muffler must be reasonably resistant to damage, corrosion and heat retention. The resonator is a secondary or substitute sound elimination component, used to augment the muffler, or in cases where space is at a premium it might even be used instead of a muffler.Catalytic converters, which became commonplace in the 1970s, are the primary and most efficient means of reducing the level of toxins in a car's exhaust. The innards of a catalytic converter (or "cat") are coated with metals. Different types of catalytic converters use different combinations of platinum, palladium and rhodium. Before the exhaust reaches the cat, it contains a potent, super-toxic combination of carbon monoxide, nitrogen oxide and hydrocarbons. (When you take your car for its emissions test, these are the chemical levels that are being tested.) When these poisons come into contact with the metals coating the inside of the cat, a chemical reaction takes place that makes the exhaust gases less harmful. As the exhaust passes through the cat, the level of chemicals should be reduced enough to comply with government regulations.

If an engine ran perfectly, it would combust all its available fuel as it ran through its cycles, converting all the dirty bits to a source of power. However, leftovers exist as pollutants because an engine simply cannot be engineered to run perfectly -- there are far too many variables. Some amount of fuel will always remain unburned or partially burned, and these remnants must be quickly processed out of the vehicle, in the form of exhaust, to make room for the next cycle of engine combustion.

As we mentioned earlier, the exhaust first exits the engine and enters the system through the exhaust manifold. From there, it travels down the system through interconnected pipes until it exits through the tailpipe, near the back bumper. The pipes themselves actually help cool the exhaust, but they're mostly a way for the exhaust to travel to (and through) the catalytic converter and muffler.

The cat has to be as close to the engine as possible, because it isn't fully functional until it rises to operating temperature. In many cases, the manufacturer places the cat shortly after the manifold, so heat from the engine helps warm the cat and quickly bring it up to temp.

After the gases pass through the cat, which will burn off and remove up to 90 percent of the exhaust's toxins, the next priority is to filter the

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engine sound [source: Allen]. The muffler and resonator are usually situated right beyond the cat. There are many variations on this combination -- some will soothe the exhaust as much as possible, while others are specifically tuned for aggressive tones. From there, the exhaust moves through the remainder of the pipes until it exits the car.

With all those chemicals swirling around, it's quite a feat that the exhaust system actually works as well as it does. A well-maintained exhaust system should last two to three years, but the pipes incur damage both inside and out. On the outside, they're susceptible to road conditions, such as impact from debris and environmental factors, such as snow, ice and road salt.

When an exhaust pipe rots through or a connection comes loose, an exhaust leak occurs. A leak is almost always immediately apparent with a loud, obnoxious sound and, possibly, drivability issues like an intermittent fluctuation in power. But, believe it or not, these aren't the real problems. It gets a little more serious if the leak occurs before the catalytic converter, which means the exhaust isn't being properly processed and all those hot chemicals are spilling everywhere into the atmosphere. It's always a good idea to get leaks fixed as soon as possible to avoid subjecting yourself, your passengers and your surroundings to unfiltered exhaust fumes.

Improved exhaust efficiency is critical to getting the most out of your car, and there are even ways to improve an older car (assuming it's in generally good condition -- a performance exhaust system won't work miracles on a total jalopy). A mechanic can usually order identical original replacement parts, but there are also alternatives from aftermarket performance parts suppliers that often give the car a facelift (at least, as much as the car's under body can be spruced up, anyway). There are several frequently-mentioned benefits of performance exhaust systems. Aftermarkets manufacturers are well aware that the auditory experience is critical to a pleasurable drive, and it also lets nearby drivers know that a little extra coin was spent on the car, too. Most manufacturers offer a variety of systems that range in sound from a subtle throatiness to an all-out roar. A good aftermarket performance exhaust can improve throttle response (how fast, and smoothly, the car reacts to the pressure applied to the gas pedal) and give a boost in horsepower. Some systems can even improve fuel economy. Performance exhausts are able to provide this power boost because they're less restrictive than stock exhausts. If the

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engine can push out more air (which also means it can take in more air) that helps the engine make more power. But contrary to what you might think, a totally free-flowing system will be counterproductive. Aftermarket exhausts are engineered to provide just the right amount of back pressure so that the engine doesn't end up running at sub-peak output. That's why it's important to choose one designed and optimized for your specific vehicle. And before you go ripping out your exhaust pipes, make sure the system you want is street-legal and won't cause your car to fail its emissions test.

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TURBOCHARGERS

A turbocharger, or turbo (colloquialism), from the Greek "τύρβη" ("turbulence") is a turbine driven forced induction device that makes an engine more efficient and produce more power for its size by forcing extra air into the combustion chamber. A turbocharged engine is more powerful and efficient than a naturally aspirated engine because the turbine forces more air, and proportionately more fuel, into the combustion chamber than atmospheric pressure alone.Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers; nowadays the term "supercharger" is usually applied to only mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that the latter is mechanically driven from the engine, often from a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine that is driven by the engine'sexhaust gas. Compared to a mechanically-driven supercharger, turbochargers tend to be more efficient but less responsive.Twincharger refers to an engine with both a supercharger and a turbocharger.In contrast to turbochargers, superchargers are mechanically driven by the engine.[12] Belts, chains, shafts, and gears are common methods of powering a supercharger, placing a mechanical load on the engine. For example, on the single-stage single-speed supercharged Rolls-Royce Merlin engine, the supercharger uses about 150 horsepower (110 kW). Yet the benefits outweigh the costs; for the 150 hp (110 kW) to drive the supercharger the engine generates an additional 400 horsepower, a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent; the engine must withstand the net power output of the engine plus the power to drive the supercharger.

Another disadvantage of some superchargers is lower adiabatic efficiency as compared to turbochargers (especially Roots-type superchargers). Adiabatic efficiency is a measure of a compressor's ability to compress air without adding excess heat to that air. The compression process always produces heat as a byproduct of that process; however, more efficient compressors produce less excess heat. Roots superchargers impart significantly more heat to the air than turbochargers. Thus, for a given volume and pressure of air, the turbocharged air is cooler, and as a result denser, containing more oxygen molecules, and therefore more potential power than the

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supercharged air. In practical application the disparity between the two can be dramatic, with turbochargers often producing 15% to 30% more power based solely on the differences in adiabatic efficiency.By comparison, a turbocharger does not place a direct mechanical load on the engine (however, turbochargers place exhaust back pressure on engines, increasing pumping losses).[12]This is more efficient because it uses the otherwise wasted energy of the exhaust gas to drive the compressor. In contrast to supercharging, the primary disadvantage of turbocharging is what is referred to as "lag" or "spool time". This is the time between the demand for an increase in power (the throttle being opened) and the turbocharger(s) providing increased intake pressure, and hence increased power.

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Key components of a turbocharger

turbocharger has three main components:

1. The turbine, which is almost always a radial inflow turbine2. The compressor, which is almost always a centrifugal compressor3. The center housing/hub rotating assembly

Twin-turbo

Twin-turbo or bi-turbo designs have two separate turbochargers operating in either a sequence or in parallel. In a parallel configuration, both turbochargers are fed one-half of the engine’s exhaust. In a sequential setup one turbocharger runs at low speeds and the second turns on at a predetermined engine speed or load. Sequential turbochargers further reduce turbo lag, but require an intricate set of pipes to properly feed both turbochargers.Two-stage variable twin-turbos employ a small turbocharger at low speeds and a large one at higher speeds. They are connected in a series so that boost pressure from one turbo is multiplied by another, hence the name "2-stage." The distribution of exhaust gas is continuously variable, so the transition from using the small turbo to the large one can be done incrementally. Twin turbochargers are primarily used in diesel engines. For example, in Opel bi-turbo diesel, only the smaller turbocharger works at low rpm, providing high torque at 1500-1700 rpm. Both turbochargers operate together in mid range, with the larger one pre-compressing the air, which the smaller on further compresses. A bypass valve regulates the exhaust flow to each turbocharger. At higher speed—2500 to 3000 RPM—only the larger turbocharger runs.Smaller turbochargers have less turbo lag than larger ones, so often two small turbochargers are used instead of one large one. This configuration is popular in engines over 2,500 CCs and in V-shape or boxer engines.

The flow range of a turbocharger compressor can be increased by allowing air to bleed from a ring of holes or a circular groove around the compressor at a point slightly downstream of the compressor inlet (but far nearer to the inlet than to the outlet).

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The ported shroud is a performance enhancement that allows the compressor to operate at significantly lower flows. It achieves this by forcing a simulation of impeller stall to occur continuously. Allowing some air to escape at this location inhibits the onset of surge and widens the operating range. While peak efficiencies may decrease, high efficiency may be achieved over a greater range of engine speeds. Increases in compressor efficiency result in slightly cooler (more dense) intake air, which improves power. This is a passive structure that is constantly open (in contrast to compressor exhaust blow off valves, which are mechanically or electronically controlled). The ability of the compressor to provide high boost at low rpm may also be increased marginally (because near choke conditions the compressor draws air inward through the bleed path). Ported shrouds are used by many turbocharger manufacturers.

Intercooling

When the pressure of the engine's intake air is increased, its temperature also increases. In addition, heat soak from the hot exhaust gases spinning the turbine may also heat the intake air. The warmer the intake air the less dense, and the less oxygen available for the combustion event, which reduces volumetric efficiency. Not only does excessive intake-air temperature reduce efficiency, it also leads to engine knock, or detonation, which is destructive to engines.Turbocharger units often make use of an intercooler (also known as a charge air cooler), to cool down the intake air. Intercoolers are often tested for leaks during routine servicing, particularly in trucks where a leaking intercooler can result in a 20% reduction in fuel economy.(Note that intercooler is the proper term for the air cooler between successive stages of boost, whereas charge air cooler is the proper term for the air cooler between the boost stage(s) and the appliance that consumes the boosted air.

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AUTOMOTIVE AERODYNAMICS

Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. For some classes of racing vehicles, it may also be important to produce down force to improve traction and thus cornering abilities.An aerodynamic automobile will integrate the wheel arcs and lights into the overall shape to reduce drag. It will be streamlined; for example, it does not have sharp edges crossing the wind stream above the windshield and will feature a sort of tail called a fastback or Kammback or liftback. Note that the Aptera 2e, the Loremo, and the Volkswagen 1-litre car try to reduce the area of their back. It will have a flat and smooth floor to support the Venturi effect and produce desirable downwards aerodynamic forces. The air that rams into the engine bay, is used for cooling, combustion, and for passengers, then reaccelerated by a nozzle and then ejected under the floor. For mid and rear engines air is decelerated and pressurized in a diffuser, loses some pressure as it passes the engine bay, and fills the slipstream. These cars need a seal between the low pressure region around the wheels and the high pressure around the gearbox. They all have a closed engine bay floor. The suspension is either streamlined (Aptera) or retracted. Door handles, the antenna, and roof rails can have a streamlined shape. The side mirror can only have a round fairing as a nose. Air flow through the wheel-bays is said to increase drag though race cars need it for brake cooling and many cars emit the air from the radiator into the wheel bay.Drag coefficientDrag coefficient (Ce) is a commonly published rating of a car's aerodynamic smoothness, related to the shape of the car. Multiplying Cd by the car's frontal area gives an index of total drag. The result is called drag area, and is listed below for several cars. The width and height of curvy cars lead to gross overestimation of frontal area.

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Today, most cars achieve a Cd of about .30. SUVs, which tend to be more boxy than cars because they're larger, accommodate more people, and often need bigger grilles to help cool the engine down, have a Cd of anywhere from .30 to .40 or more. Pickup trucks -- a purposefully boxy design -- typically get around .40 

Measuring Drag Using Wind Tunnels

To measure the aerodynamic effectiveness of a car in real time, engineers have borrowed a tool from the aircraft industry -- the wind tunnel.

In essence, a wind tunnel is a massive tube with fans that produce airflow over an object inside. This can be a car, an airplane, or anything else that engineers need to measure for air resistance. From a room behind the tunnel, engineers study the way the air interacts with the object, the way the air currents flow over the various surfaces.

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The car or plane inside never moves, but the fans create wind at different speeds to simulate real-world conditions. Sometimes a real car won't even be used -- designers often rely on exact scale models of their vehicles to measure wind resistance. As wind moves over the car in the tunnel, computers are used to calculate the drag coefficient (Cd).However, in recent years, the big, multi-million-dollar wind tunnels are being used less and less. Computer simulations are starting to replace wind tunnels as the best way to measure the aerodynamics of a car or aircraft. In many cases, wind tunnels are mostly just called upon to make sure the computer simulations are accurate.There's more to aerodynamics than just drag -- there are other factors called lift and down force, too. Lift is the force that opposes the weight of an object and raises it into the air and keeps it there. Downforce is the opposite of lift -- the force that presses an object in the direction of the ground.

You may think that the drag coefficient on a Formula Oneracecar would be very low -- a super-aerodynamic car is faster, right? Not in this case. A typical F1 car has a Cd of about .70.

Why is this type of racecar able to drive at speeds of more than 200 miles an hour (321.9 kilometers per hour), yet not as aerodynamic as you might have guessed? That's because Formula One cars are built to generate as much downforce as possible. At the speeds they're

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traveling, and with their extremely light weight, these cars actually begin to experience lift at some speeds -- physics forces them to take off like an airplane. Obviously, cars aren't intended to fly through the air, and if a car goes airborne it could mean a devastating crash. For this reason, downforce must be maximized to keep the car on the ground at high speeds, and this means a high Cd is required.

Formula One cars achieve this by using wings or spoilers mounted onto the front and rear of the vehicle. These wings channel the flow into currents of air that press the car to the ground -- better known as downforce. This maximizes cornering speed, but it has to be carefully balanced with lift to also allow the car the appropriate amount of straight-line speed.

A spoiler is an automotive aerodynamic device whose intended design function is to 'spoil' unfavourable air movement across a body of a vehicle in motion, usually described as turbulence or drag. Spoilers on the front of a vehicle are often called air dams, because in addition to directing air flow they also reduce the amount of air flowing underneath the vehicle which generally reduces aerodynamic lift and drag. Spoilers are often fitted to race and high-performance sports cars, although they have become common on passenger vehicles as well. Some spoilers are added to cars primarily for styling purposes

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and have either little aerodynamic benefit or even make the aerodynamics worse.The term "spoiler" is often mistakenly used interchangeably with "wing". An automotive wing is a special type of spoiler whose intended design is to generate Downforce as air passes around it, not simply disrupt existing airflow patterns. As such, rather than decreasing drag wings actually increase drag.The goal of many spoilers used in passenger vehicles is to reduce drag and increase fuel efficiency. Passenger vehicles can be equipped with front and rear spoilers. Front spoilers, found beneath the bumper, are mainly used to decrease the amount of air going underneath the vehicle to reduce the drag coefficient and lift.Sports cars are most commonly seen with front and rear spoilers. Even though these vehicles typically have a more rigid chassis and a stiffer suspension to aid in high speed manoeuvrability, a spoiler can still be beneficial. This is because many vehicles have a fairly steep downward angle going from the rear edge of the roof down to the trunk or tail of the car which may cause air flow separation. The flow of air becomes turbulent and a low-pressure zone is created, increasing drag and instability (Bernoulli effect). Adding a rear spoiler could be considered to make the air "see" a longer, gentler slope from the roof to the spoiler, which helps to delay flow separation and the higher pressure in front of the spoiler can help reduce the lift on the car by creating Downforce. This may reduce drag in certain instances and will generally increase high speed stability due to the reduced rear lift.Material:Spoilers are usually made of lightweight polymer-based materials, including:

ABS plastic : Most original equipment manufacturers produce spoilers by casting ABS plastic with various admixtures, typically granular fillers, which introduce stiffness to this inexpensive material. Frailness is a main disadvantage of plastic, which increases with product age and is caused by the evaporation of volatile phenols.

Fiberglass : Used in car parts production due to the low cost of the materials. Fiberglass spoilers consist of fiberglass cloth infiltrated with a thermosetting resin, such as epoxy. Fiberglass is sufficiently durable and workable, but has become unprofitable for large-scale production because of the labor involved.

Silicon : More recently, many auto accessory manufacturers are using silicon-organic polymers. The main benefit of this material is

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its phenomenal plasticity. Silicon possesses extra high thermal characteristics and provides a longer product lifetime.

Carbon fiber : Carbon fiber is lightweight, durable, but also expensive. Due to the large amount of manual labor, large-scale production cannot widely use carbon fiber in automobile parts currently.

Other common spoiler types

Front spoilers: A front spoiler (air dam) is positioned under or integrated with the front bumper. In racing, this spoiler is used to control the dynamics of handling related to the air in front of the vehicle. This can be to improve the drag coefficient of the body of the vehicle at speed, or to generate downforce. In passenger vehicles, the focus shifts more to directing the airflow into the engine bay for cooling purposes.

Truck bed spoiler: This attaches only to the top of the truck bed rails near the rear. Used with a bed cover, this spoiler is intended to reduce the air profile of the steep drop-off from the tailgate.

Truck cab spoiler: This is purposed the same as above, except focusing on the drop-off from the cab of the truck.

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DIFFERENTIAL

The differential has three jobs: To aim the engine power at the wheels To act as the final gear reduction in the vehicle, slowing the

rotational speed of the transmission one final time before it hits the wheels

To transmit the power to the wheels while allowing them to rotate at different speeds

Car wheels spin at different speeds, especially when turning. You can see from the animation that each wheel travels a different distance through the turn, and that the inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the distance travelled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.For the non-driven wheels on your car -- the front wheels on a rear-wheel drive car, the back wheels on a front-wheel drive car -- this is not an issue. There is no connection between them, so they spin independently. But the driven wheels are linked together so that a single engine and transmission can turn both wheels. If your car did not have a differential, the wheels would have to be locked together, forced to spin at the same speed. This would make turning difficult and hard on your car: For the car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a great deal of force is required to make a tire slip. That force would have to be transmitted through the axle from one wheel to another, putting a heavy strain on the axle components.The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.

The differential is found on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles. These all-wheel-drive vehicles need a differential between each set of drive

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wheels, and they need one between the front and the back wheels as well, because the front wheels travel a different distance through a turn than the rear wheels.

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Part-time four-wheel-drive systems don't have a differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed. This is why these vehicles are hard to turn on concrete when the four-wheel-drive system is engaged.

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When a car is driving straight down the road, both drive wheels are spinning at the same speed. The input pinion is turning the ring gear and cage, and none of the pinions within the cage are rotating -- both side gears are effectively locked to the cage.

Note that the input pinion is a smaller gear than the ring gear; this is the last gear reduction in the car. You may have heard terms like rear axle ratio or final drive ratio. These refer to the gear ratio in the differential. If the final drive ratio is 4.10, then the ring gear has 4.10 times as many teeth as the input pinion gear.

Differentials and Traction

The open differential always applies the same amount of torque to each wheel. There are two factors that determine how much torque can be applied to the wheels: equipment and traction. In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground. If you give the car more gas after the wheels start to slip, the wheels will just spin faster.

On Thin Ice

If you've ever driven on ice, you may know of a trick that makes acceleration easier: If you start out in second gear, or even third gear, instead of first, because of the gearing in the transmission you will have less torque available to the wheels. This will make it easier to accelerate without spinning the wheels.

Now what happens if one of the drive wheels has good traction, and the other one is on ice? This is where the problem with open differentials comes in.

Remember that the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. It doesn't take much torque to make a tire slip on ice. And when the wheel with good traction is only getting the very small amount of torque that can be

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applied to the wheel with less traction, your car isn't going to move very much.

Off Road

Another time open differentials might get you into trouble is when you are driving off-road. If you have a four-wheel drive truck, or an SUV, with an open differential on both the front and the back, you could get stuck. Now, remember -- as we mentioned on the previous page, the open differential always applies the same torque to both wheels. If one of the front tires and one of the back tires comes off the ground, they will just spin helplessly in the air, and you won't be able to move at all.

The solution to these problems is the limited slip differential (LSD), sometimes called positraction. Limited slip differentials use various mechanisms to allow normal differential action when going around turns. When a wheel slips, they allow more torque to be transferred to the non-slipping wheel.

Clutch-type Limited Slip Differential

The clutch-type LSD is probably the most common version of the limited slip differential

This type of LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches. Some of these have a cone clutch that is just like the synchronizers in a manual transmission.

The spring pack pushes the side gears against the clutches, which are attached to the cage. Both side gears spin with the cage when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn. The clutches fight this behaviour, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch. The stiffness of the springs combined with the friction of the clutch determines how much torque it takes to overpower it.

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Getting back to the situation in which one drive wheel is on the ice and the other one has good traction: With this limited slip differential, even though the wheel on the ice is not able to transmit much torque to the ground, the other wheel will still get the torque it needs to move. The torque supplied to the wheel not on the ice is equal to the amount of torque it takes to overpower the clutches. The result is that you can move forward, although still not with the full power of your car.

When a car is turning, the difference in speed between the wheels is not as large as when one wheel is slipping. The faster the plates are spinning relative to each other, the more torque the viscous coupling transfers. The coupling does not interfere with turns because the amount of torque transferred during a turn is so small. However, this also highlights a disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually starts slipping.

A simple experiment with an egg will help explain the behaviour of the viscous coupling. If you set an egg on the kitchen table, the shell and the yolk are both stationary. If you suddenly spin the egg, the shell will be moving at a faster speed than the yolk for a second, but the yolk will quickly catch up. To prove that the yolk is spinning, once you have the egg spinning quickly stop it and then let go -- the egg will start to spin again (unless it is hard boiled). In this experiment, we used the friction between the shell and the yolk to apply force to the yolk,

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speeding it up. When we stopped the shell, that friction -- between the still-moving yolk and the shell -- applied force to the shell, causing it to speed up. In a viscous coupling, the force is applied between the fluid and the sets of plates in the same way as between the yolk and the shell.

FUEL INJECTION SYSTEM

For most of the existence of the internal combustion engine, the carburetor has been the device that supplied fuel to the engine. On many other machines, such as lawnmowers and chainsaws, it still is. But as the automobile evolved, the carburetor got more and more complicated trying to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits:

Main circuit - Provides just enough fuel for fuel-efficient cruising Idle circuit - Provides just enough fuel to keep the engine idling Accelerator pump - Provides an extra burst of fuel when the

accelerator pedal is first depressed, reducing hesitation before the engine speeds up

Power enrichment circuit - Provides extra fuel when the car is going up a hill or towing a trailer

Choke - Provides extra fuel when the engine is cold so that it will startIn order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop control -- it was not feasible to achieve this control with carburetors. There was a brief period of electrically controlled carburetors before fuel injection systems took over, but these electrical carbs were even more complicated than the purely mechanical ones.At first, carburetors were replaced with throttle body fuel injection systems (also known as single point or central fuel

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injection systems) that incorporated electrically controlled fuel-injector valves into the throttle body. These were almost a bolt-in replacement for the carburetor, so the automakers didn't have to make any drastic changes to their engine designs.Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel injection (also known as port, multi-point or sequential fuel injection). These systems have a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and quicker response.

When you step on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU, the computer that controls all of the electronic components on your engine) "sees" the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it.Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.

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A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.

When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel -- to make as fine a mist as possible so that it can burn easily.

Engine SensorsIn order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few:

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Mass airflow sensor - Tells the ECU the mass of air entering the engine

Oxygen sensor(s)  - Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly

Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary

Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature

Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)

Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold

The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.

Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse widthThere are two main types of control for multi-port systems: The fuel injectors can all open at the same time, or each one can open just before the intake valve for its cylinder opens (this is called sequential multi-port fuel injection).The advantage of sequential fuel injection is that if the driver makes a sudden change, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine.The algorithms that control the engine are quite complicated. The software has to allow the car to satisfy emissions requirements for 100,000 miles, meet EPA fuel economy requirements and protect engines against abuse. And there are dozens of other requirements to meet as well.The engine control unit uses a formula and a large number of lookup tables to determine the pulse width for given operating conditions. The equation will be a series of many factors multiplied by each other. Many of these factors will come from lookup tables. We'll go through a simplified calculation of the fuel injector pulse width. In this example, our equation will only have three factors, whereas a real control system might have a hundred or more.

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Pulse width = (Base pulse width) x (Factor A) x (Factor B)

COST SHEET

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