Cat-back exhaust systems will include any pipes that run from the catalytic converter to the muffler, the muffler itself, any pipes that may run from the muffler to the exhaust tips, and the exhaust tips themselves. Some cat-back exhaust systems have a muffler 6.7 cummins egr delete kit, which means no muffler is included. This is typically found on vehicles that function primarily for off-road use