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 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 - at the catalytic converter and downpipe.

The second effect, less heavily marketed but more durable, concerns weight and durability. A stainless steel exhaust does not rust, can still be removed in ten years, and weighs less than an original aluminized-steel exhaust. On a car you intend to keep, it is the part you only have to install once.