A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is acoustic: less baffled mufflers, a more pronounced low-pitched tone, and a sharper-sounding rise in revs. In terms of power, the gain does exist 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 system does not rust, can still be removed ten years from now, and weighs less than an original aluminized steel exhaust. On a car you intend to keep, it is the part you only install once.