A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is acoustic: less-restricted silencers, a more pronounced low-pitched tone, and a more responsive-sounding climb through the rev range. In terms of power, the gain exists but remains modest on a stock engine because the restriction in a standard engine is mainly upstream - the catalytic converter and downpipe.

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