People modify a car’s exhaust mainly to reduce flow restrictions (lower back-pressure), change its acoustic character, and improve engine efficiency under tuned conditions. By selecting different muffler types, pipe diameters, resonators, or using headers and high-flow catalytic converters, tuners can shift where in the RPM band torque and power peaks occur, as well as alter throttle response and the exhaust note. When combined with ECU remaps or “tune” adjustments, the engine’s fuel/ignition ti