1. CONTENTS
Sr. 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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2. 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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3. 13 Fuel Injection System
14 Cost Sheet
15 Performance Charts
16 Conclusion
About Team RPM
3

4. 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 read an
4

5. 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.
5

6. Back pressure and velocity
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 pressure with a much
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7. 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.
Exhaust theory
7

8. 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 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:
8

9. 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.
9

10. 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 from the combustion
10

11. 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
11

12. 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.
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
12

13. 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.
13

14. 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.
14

15. 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 called constructive
interference. But, if they are exactly out of phase, they add up to zero.
15

16. 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 another
component in the exhaust that looks like a muffler, but is called a
16

17. 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 pressure
pulses. A steel housing surrounds the insulation
.
17

18. 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.
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
18

19. 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 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
19

20. 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.
Characteristics
The 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 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 PISTON
A 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
20

21. 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 Pattern
The 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 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
21

22. 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).
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.
22

23. 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
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
23

24. 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
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
24

25. 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.
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.
25

26. 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.
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
26

27. 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
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-E
VTEC-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).
27

28. 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).
Stage 3 – VTEC
From ~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.
28

29. 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
29

30. to the US on the Honda Odyssey Mini Van, and can now be 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
30

31. heads for decades before multivalve heads appeared, however 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.
31

32. Components
Drum brake components include the backing plate, brake drum, shoe,
wheel cylinder, and various springs and pins.
Backing plate
The 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.
32

33. Back plate made in the pressing shop.
Brake drum
The 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 cylinder
One 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 shoe
Brake 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, hold-
33

34. 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.
34

35. 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-servo effect and
35

36. 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.
Run-out
Run-out is measured using a dial indicator on a fixed rigid base, with the
36

37. 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 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
37

38. 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.
38

39. 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,
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.
39

40. 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.
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
40

41. resulting in engines that often claim the legal maximum of 64 PS (47 kW;
63 bhp).
Piston speed
An 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
41

42. 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 use
Most 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.
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)
42

43. 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.
43

44. 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 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.
44

45. Working of ECU
Control of Air/Fuel ratio
For 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 timing
A 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 speed
Most 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
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.
45

46. Control of variable valve timing
Some 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 control
Experimental 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 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
46

47. 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
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
47

48. 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 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.
48

49. 49

50. AIR INTAKE SYSTEM
There 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.
50

51. 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.
51

52. 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.
52

53. 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 dampens
the movement of the vane giving a more accurate measurement.
53

54. 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 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
54

55. 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 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
55

56. 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.
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
56

57. 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.
57

58. 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 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.
58

59. 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.
59

60. EXISTING EXHAUST SYSTEM IN DETAIL
An 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.
Terminology
Manifold 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 the common outlet all equal length,
and joined at narrow angles to encourage pressure waves to flow through
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