By Jim Kerr
Exhaust systems on most vehicles are a compromise. Besides carrying the exhaust fumes away from the passenger compartment, they also have to reduce emissions, muffle the noise and also fit around the body, suspension and drivetrain components. Over the past several years, the auto manufacturers have paid a lot of attention to exhaust system design, as it is one way to improve fuel efficiency and power without adding stress to engine components. Even so, they have to keep manufacturing costs down. That is where the aftermarket manufacturers step in with performance exhaust systems.
In a typical exhaust system, the gases flow from the engine through exhaust manifolds. They are then fed into a catalytic converter (some vehicles with V6 or V8 engines use two converters) and then into a muffler. Most vehicles come with a single exhaust pipe that feeds a single muffler near the back of the vehicle. Dual exhaust outlets are a frequently seen styling feature on many vehicles, but usually both outlets come from a common muffler.
The most common type of aftermarket performance system is called a “cat-back” system. These systems replace the factory system after the catalytic converter. By leaving the converter in place, the vehicle still meets the emission standards. The cat-back system often uses larger diameter pipe that is routed to minimize bends. Where bends are required, a mandrel bender is used to create smooth curves in the pipe. A conventional exhaust tubing bender compresses the pipe on the inside of the bend. The pipe will be reduced in diameter and have several wrinkles on the inside radius that restricts gas flow. Smooth mandrel bends flow better and look better too when showing off your ride!
Cat-back systems also include the muffler. By increasing the size of the muffler, there is more room for the exhaust gases to expand and this increases flow. Large is good! The muffler may have different internal passages that also allow more exhaust flow. This can change the tone of the exhaust note and the volume, which some drivers prefer. A high-performance cat-back system doesn’t have to be noisy however, and if you drive a lot of highway miles you will appreciate a quieter exhaust system.