Tunning
How to tune cars to make them go faster
 

Nowadays due to the increasing sound pollution and air pollution cars are being restricted to lesser horses, however with a few minor tweakings you can get the best out of your machine.

 

Here is how: -

 

Cold Air Intake with Air Filter - Cold Air Intakes also known as CAI's. You cars stock air box is highly restrictive for air. It doesnot let more air come. Also the stock OE filters are made of paper as its cheaper. There are a few companies which make performance air filters like Green, KnN, Pipercross, Ractive, etc. These airfilters are made of better material like Cotton and let more air get inside the engine. When more air gets inside the engine the cars AFR runs richers and injects more fuel and thereby increasing power.

 

Header

The header has the greatest effect on the power band and ultimate power production of a non-turbo car. There are MANY factors that go into a properly designed header. One factor is the way you join the pipes together. The two possible configurations for a 4 cylinder are 4-2-1 and 4-1. Basically a 4-2-1 design joins two primaries together into a secondary pipe, and then joins the two secondaries together. A 4-1 design joins all four at the same time. Both have advantages, but the 4-1 design allows the gas pulses to interact in a way that makes the best torque. Here is a simple drawing to help visualize the two different styles.

 

Primary Pipe Diameter -Smaller diameters keep velocity higher with smaller exhaust volumes. The more exhaust you are trying to push out the larger the primaries need be. The volume of gasses that you need to flow depends on displacement, RPM, and load. The more displacement you have per cylinder the larger the primaries need to be. The same is true for RPM, the more RPM you will be turning, the more diameter you will need as you will be pushing out a lot of volume over time. Higher loads on the motor also create a higher volume of gasses. As with every other variable there is a balance to be kept. If you are not flowing enough gasses for the pipe diameter (pipes are too big) the gasses will loose their velocity If the gasses get too slow you loose torque, and if you go way to large you can even loose top end power as well. Get it right and you get the best of both worlds, good low end torque and good top end power.

Primary Pipe Length -This has a huge effect on the powerband. Generally longer primaries make better low end while shorter lengths move the powerband up in the RPM range. The length affects the powerband by timing when pressure waves reach the cylinder. To put it as simply as possible, the pressure wave comes out of the cylinder and travels down the primary pipe until it hits the collector. There it gets reflected back down the primary pipe as a negative wave. When it hits the cylinder it helps pull more exhaust gasses out of the cylinder and pull more air in to the cylinder. Since power is made by mixing air and fuel and then exploding it, more air and fuel make more power. This effect is known as scavenging and is one of the main goals of a well designed header. Equal length primaries help each exhaust pulse pull the one behind it. This helps create a suction in a sense. Instead of just relying on the pressure of the exhaust stroke of the motor to get the spent gasses out, the suction of the pulse in front of it helps pull it out. One factor some header designers forget when trying to design an equal length header for the Subaru is that the length of the exhaust port is effectively part of the header and needs to be accounted for. Complicating this is the fact that the exhaust ports on the Subaru are not the same lengths. Not accounting for this effects power production. Below is a simple drawing of the port layout. You can see that Cylinder A has a longer path than Cylinder B.

 

You can see how getting the length correct is where most of the time is spent during testing.

Collector Type -The collector merges all of the primary pipes together. There are designs ranging from cheap and simple to incredibly complex and costly. If you just joined the pipes in the simplest possible way you would have something that resembled the picture on the right.

 

The dead space in the middle of all of the pipes would cause a lot of turbulence and hinder flow. Eliminating the dead space is the main advantage of the merge collector. The image on the right is an example of a way that you can form the pipes to make a cross pattern in the center. This is a more cost effective way to make the pipes join smoothly. Not quite as elegant as the merge collector, but still very good. You can see that the dead space in the center is virtually eliminated.

The bad daddy of all collectors is the merge collector. It is from Burns Stainless and is one of the finest collectors you can buy. Note how all of the pipes are joined in a smooth way to avoid turbulence.

 

Collector Length -The length of the collector also plays a role in determining the powerband of the motor. Generally the longer the collector the more the powerband is shifted up. You also want enough length in the collector to smoothly join the gasses coming from the primary pipes. If the junction is too abrupt they do not interact very well causing turbulence, and again hindering flow. This is also another area of a lot of testing. The volume of the collector has a fairly big effect on the powerband of the motor.

 

Collector Width -The width of the collector helps control how well the exhaust pulses interact with each other. Make it too big and one pulse cannot help pull the next very well and the gasses can stagnate hurting flow. Make it too small and you hinder flow by causing too much backpressure. Yet another area to test.

Taper Angles - Basically you want the least amount of abrupt changes as possible. This mostly applies to the collector where it necks down to the diameter the exhaust will be. You do not want an abrupt angle as it will hinder flow.

The entries into the primary pipes from the head also have to be as close to the diameter of the exhaust ports as possible. This is so that you do not get yet another area for turbulence to get in the way of things. Protrusions into the gas flow should be avoided here most of all, as they have a much larger effect than in any other point in the system. According to many experts that do not play the marketing game, the stepped header designs are an attempt to cure other problems inherent in the design. The steps also add complexity and cost.

The lay-out of the car dictates a lot of how the header is made. The ports being on opposite sides of the Subaru engine do not make things easy when designing a header for our cars. Each change in length during testing requires almost making a new header on a Subaru boxer motor, thus the rather lengthy design process of our header. Getting lengths equal is definitely a big task given the packaging, and any variance within .5-1" is considered the mark of a top notch header designer.

 

Catalytic Converter

We have actually tested cat and catless on non-turbo cars as well. If you use a well designed cat there is very little power to be gained by not having a cat. The cat is a place where abrupt angles make a huge difference. Since inside the cat you are making drastic changes going from the diameter of the pipe, into a large diameter area inside the cat, and back to the diameter of the pipe having abrupt angles can really slow things down. This is as true for turbo as it is for non-turbo cars. You also want the gasses spreading out to flow across the complete area of the catalyst bricks of the cat. If the gasses are too concentrated on one part of the cat you will not be able to flow to the full potential of the catalyst bricks. That is why you see the gentle angle at the beginning of the "good" cat rather than at the end of the less optimal "better" cat.

 

 

Cat-back

Designing a good cat-back is fairly simple compared to the header. Keeping velocity high is still the goal. Pipe that is too large will loose low end torque as the gas starts moving slower. Pipe that is too small will loose top end power. So again there is a balance to be reached. The same rule applies to keeping the piping smooth and using proper bending techniques. The muffler needs to be as free flowing as possible without being too loud. Besides that there is not a lot of complexity in a cat-back. It is definitely easier to design than a header.


High performance modifications to the flywheel and clutch centre on weight reduction and, because the parts are rotating masses, have benefits over and above any saving in mass alone. Weight savings to the flywheel and clutch improve three aspects of performance: acceleration, deceleration, and cornering (more so than you might expect in respect of acceleration).
Warning! - Performance aspects aside, there are safety considerations when modifying the flywheel.
For the clutch, modifications to increase clamping pressure improve no performance aspect, but are necessary if clutch problems and failures, due to increased engine power output, are to be avoided.

Flywheel
The flywheel is fitted on the end of the crankshaft to store energy from the firing stroke of every cylinder. In addition, it carries the toothed ring gear that the starter motor pinion engages to turn the engine. Last, but not least, it provides the mating face for the clutch plate and a fastening surface for the clutch cover.

Lightening & balancing
You may have heard that lightening the flywheel will cause problems with engine tickover. There are two responses to this: (a) it probably won’t, and (b) tickover is hardly important on a tuned engine anyway. The fact is that changing the cam to one with a greater overlap than standard will have a greater effect on tickover than just about anything you can do to the flywheel. In addition, if the flywheel is re-balanced, the tickover may well be smoother than with the standard flywheel.
The reason why flywheels are lightened is that not only are they a heavy mass (weight) in their own right but, as part of the reciprocating mass of the engine, they have to be accelerated in their own right. Less weight requires less energy to move and therein lies the improvement in performance. A weight reduction of the flywheel can be equivalent to fifteen times the weight reduction of the all up weight of the car. In practical terms, ten pounds off the flywheel can have the same effect as reducing the weight of the car by 150 pounds. But this is only the case for acceleration in first gear - pretty important for a racing start on the circuit, less so for traffic light grand prix. An approximate formula for working out the benefit of flywheel weight reduction is:

0.5 x r2 x g2 + R2 divided by R2 = weight of the car lbs/1lb flywheel weight.
(r = radius of gyration. g = gearbox ratio x final drive ratio. R = radius of wheel + tyre.)

If you are lightening the flywheel yourself note that the most important place for the weight to come off is at the outer radius rather than the centre. Caution! - Also, note that although you may wish to lightly reface the clutch mating face of the flywheel, a serious removal of metal here will cause problems with clutch set up heights and is, therefore, to be avoided.
Balancing is beneficial because it reduces vibration and stresses on the engine. Warning! - It is not unknown for unbalanced flywheels to disintegrate; this can also happen with poorly or excessively lightened flywheels. Parts of a disintegrating flywheel can tear through the bellhousing and bodywork like shards from a grenade.

More mods like Turbo, Porting Polishing will be up here for reading soon.