Cat-back exhaust systems replace the portion of the exhaust system behind the catalytic converter. This can improve performance by reducing exhaust backpressure, potentially leading to increased horsepower and torque. Cat-back systems can also alter the exhaust note, offering a more sporty sound for some drivers. When choosing a cat-back exhaust, consider material (such as stainless steel for durability), pipe diameter (wider can improve performance but may increase noise), and sound profile (ensure it aligns with local regulations and your preferences).