Why to install an aftermarket exhaust system..

A low restriction exhaust system - following the turbine on a turbo car, or following the manifold/extractors on the remainder of cars - is a prerequisite to making good power. In most cases, a high-flow exhaust system should also be amongst your initial group of modifications, since it's a relatively low-cost and bolt-on modification.

Exhaust backpressure behind any tuned-length manifold/extractor system is detrimental to making power. It should be minimised as much as possible.

Reducing exhaust backpressure serves to improve exhaust gas evacuation from the combustion chamber, enabling more of each new air/fuel charge to be inhaled into the combustion chamber. The more fresh air and fuel burnt, the more power you'll enjoy.

Another benefit of a low restriction exhaust system is a reduction of pumping losses - in other words, not as much power is required for the piston to force the burnt gasses out the open exhaust valve(s).

The on-road benefits associated with a high-flow exhaust system cannot be understated - it gives the potential for improved throttle response, increased torque and top-end power. Fuel consumption can also be improved, depending largely on your driving style.