A complete system replaces everything downstream of the catalytic converter. Its main effect is sound: less restrictive silencers, a deeper tone and a more noticeable rise in revs to the ear. In terms of 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 mentioned and more lasting: weight and durability. A stainless-steel system does not rust, can still be removed in ten years and weighs less than a standard aluminised-steel exhaust. On a car you intend to keep, it is the part you only install once.