Exhaust systems are a vital part of a car's performance and efficiency. They channel exhaust fumes away from the engine and passengers, and can also influence horsepower and torque. When choosing an exhaust system, consider factors like material, diameter, and sound output. In terms of material, stainless steel offers durability and corrosion resistance, while mandrel-bent piping improves exhaust flow. A larger diameter can improve performance but may increase noise, while a smaller diameter can reduce noise but restrict flow.