A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is sound: less-restricted mufflers, a more pronounced low tone, and a crisper-sounding rise in revs. In terms of 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 durable: weight and durability. A stainless steel exhaust does not rust, can still be removed ten years from now, and weighs less than a stock aluminized-steel exhaust. On a car you plan to keep, it is the part you only install once.