The cat back portion of the exhaust system generally refers to the section back of the rear catalytic converter. This includes the resonator, rear exhaust pipe, muffler and tip.

The resonators main purpose is to attenuate the sound of high pressure exhaust gases being forced through the system. Sophisticated units are designed to internally reflect the sound waves so that they collide with one another and cancel out, deadening the noise significantly. It is possible to purchase units that will produce a low growl instead, though this is more for style purposes than practicality.

A muffler is designed to do a similar job to the resonator, albeit to a greater degree. The most basic muffler works on the absorption principle, and uses materials such as fibreglass or steel wire to absorb much of the sound before the exhaust gases are expelled. Another common type of muffler works by restricting the flow of exhaust gases which drastically cuts down on noise. However, this also reduces the efficiency of the exhaust system and ultimately the efficiency of the engine. Finally, more sophisticated mufflers work using the same reflection principles as the resonator combined with absorption materials. These are the best performing mufflers available and provide the greatest reduction in noise possible.

The tip is little more than an outlet for the exhaust gases and come in a variety of shapes and sizes. Most are designed for little more than their sound and visual appearance. It is wise to match up diameters along your exhaust system for best performance, so it isn't always necessary to fit the biggest exhaust tip you can find!

Replacing your cat back system can help improve engine performance and fuel economy albeit to a very small degree. By selecting a system with the appropriate diameter pipes and a less restrictive muffler, you can allow gases to flow more freely and reduce the effort required by the engine to force the gases through the exhaust system.

High performance cat back exhaust systems also feature coated pipes, designed to keep the exhaust gases hot as they pass through the system. This again boils down to density, as hotter gases are easier to force through the exhaust system than cool gases. Bear in mind that larger diameter pipes are not always better, as there comes a point when having too larger exhaust pipe will actually inhibit the flow of exhaust gases.

To get the best performance out of your exhaust system you will also need to replace the exhaust manifold with a header. This aids the flow of exhaust gases away from the engine thus reducing the energy lost expelling gas further still, though this is extra work and inevitably extra cost. If you're looking for a marginal improvement on performance and a better sound then a cat back system is ideal. If you are looking for a real performance boost however, you will need to go one better and replace the entire exhaust system from manifold to tailpipe.