Stainless steel exhaust system either 1 × 80 mm for BMW/Mini Cooper S — TA Technix

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 immediate-sounding climb through the rev range. In terms of power, the gain exists but remains modest on a stock engine, because the restriction in a production engine is mainly upstream - the catalytic converter and downpipe.

The second effect, less commonly mentioned but 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 standard aluminized-steel exhaust. On a car you plan to keep, it is the part you only install once.