Performance Exhaust explained

Explanation

Performance Exhaust systems are a collection of altered and/or improved parts that add up to make an entire exhaust system and replaces what would have been a regular system.
Performance exhaust is often referred to as aftermarket exhaust because it is relatively easy to acquire aftermarket exhaust upgrades. In fact it is much more common to see vehicles with aftermarket exhaust parts than vehicles with performance exhaust from the factory.
A brief explanation on the regular exhaust system will be helpful in understanding the performance exhaust. A basic exhaust system is used to reduce noise (silencer/muffler), reduce emissions (catalytic converter) and to measure the oxygen content (sensors) as the gases leave the engine.

Reducing noise and emissions restricts the free flow of the exhaust gases and this creates a back pressure all the way back to the engine and affects the four stroke cycle.
Performance exhaust increases peak horsepower by reducing the amount of back pressure the exhaust sends by allowing a free flow of the gasses from the engine to the outside of the vehicle.
Several methods can be used to achieve this free flow. One way is using a type of manifold called a header. This uses individual pipes from each cylinder of approximately the same length that merges into the down pipe and smoother curves.

The equal length of the pipes creates a vacuum effect that pulls the gases out of the cylinder on each exhaust stroke then the smoother curves means less resistance of the airflow.
Another way is by increasing the diameter of the downpipe and also using a minimum amount of curves and smooth angles for the few curves it may have. The muffler/silencer is also altered to reduce the back pressure and ultimately does less silencing.
This change of sound from the vehicle results in a more desirable sound for a performance oriented vehicle. Some exhausts systems are even acoustically tuned to increase the noise and give the vehicle a louder or unique sporty sound especially during accelerating, downshifts or even when you take your foot off the accelerator pedal.
Aftermarket exhausts also creates a visual appeal as the muffler of the vehicle will be different from a muffler on a non performance vehicle. There are persons who change the muffler on their vehicle just for that visual effect and the performance/aftermarket muffler is one method of identifying the vehicle as performance oriented.
In any exhaust system the airflow and back pressure must be controlled as reducing back pressure increases peak horsepower but it reduces low end torque at low speed.
Some performance exhaust systems use two stage mufflers with internal valves that can restrict airflow at low revs but at higher revs and speeds when too much pressure starts to back up the valve opens to allow a free flow.

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