A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is sound: less restrictive mufflers, a deeper tone, and a more pronounced rise in revs to the ear. 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 mentioned but more long-lasting: weight and durability. A stainless steel exhaust does not rust, can still be removed ten years from now, and weighs less than a factory aluminized-steel exhaust. On a car you plan to keep, it is the part you only install once.