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

The second effect, less often advertised but more lasting, concerns weight and durability. A stainless steel exhaust 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.