“Cat back” refers to the section of the exhaust system that runs from the outlet of the catalytic converter to the exhaust tips. A cat back exhaust kit usually includes the pipe from the converter to the muffler, the muffler, and the exhaust tips. They generally use larger diameter pipe than a stock system. The better systems have mandrel-bent turns. Mandrel bending works much like a flexible straw. When the straw is bent, a flexible section of the straw expands to maintain the round opening. Mandrel bending allows the hot exhaust gases to flow with less turbulence, giving you more power.