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