The term cat back exhaust can be defined as the section of an exhaust system that attaches after the last catalytic converter in the system. It is typically made up of a rear-pipe, a resonator and a muffler, but depending on the make and model, it can also include a mid-pipe, X-pipe, H-Pipe or a Y-Pipe.
Adding an aftermarket cat back can provide several benefits, the first of which is more power. Aftermarket exhaust systems are designed to be freer flowing than your stock exhaust, usually incorporating larger diameter piping and higher-grade mandrel bent tubing for a more laminar flow. These changes can result in a reduced level of back pressure at the engine manifold, which means the engine can breathe a little easier and release more horsepower and torque. How much horsepower is gained depends highly on the design of your factory exhaust system and the quality of the statistical converters in front of it. If the stock catalytic converters are fairly restrictive, then less power can be gained from a cat back exhaust system. If the stock cat's flow a large amount of exhaust gas with creating too much restriction, then a cat back exhaust system should offer a nice increase in power.
An increase in fuel economy is often experienced after installation. This is the result of the engine not have to work as hard pushing exhaust gases through the piping. This reduces the total amount of load on the engine, causing higher efficiency and MPG. This increase in fuel economy typically occurs when traveling at freeway speeds, but can sometimes be noticed when driving in the city as well.
Another big benefit of a cat back exhaust system is the sound they can produce. Whether you want just a little more grunt or a full-on growl, there is a system out there that will satisfy your ears. This is actually a very big consideration when purchasing, so make sure to do your homework first. There's nothing worse than spending a lot of time installing an auto part only to find out it is not what you wanted.