A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is sound: less-restricted mufflers, a more pronounced low tone, and a more assertive-sounding climb through the rev range. In terms of power, the gain exists but remains modest on a stock engine, because the main restriction on a standard engine is upstream - 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 ten years from now, and weighs less than an original aluminized-steel exhaust. On a car you plan to keep, it is the part you only install once.