A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is sound: less baffled mufflers, a more pronounced low tone, and a sharper-sounding climb through the rev range. As for power, the gain exists but remains modest on a stock engine, because the restriction in a production engine is mainly upstream - the catalytic converter and downpipe.

The second effect, less often advertised and more lasting: weight and durability. A stainless steel exhaust does not rust, can still be removed ten years from now, and weighs less than a factory aluminized-steel exhaust. On a car you plan to keep, it is the part you only install once.