Stainless steel exhaust system 2 × 70 mm for BMW 325i/330i E90 sedan /E91 Touring — 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 tone and a sharper-sounding rev build-up. As for 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 advertised 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 stock aluminized steel exhaust. On a car you plan to keep, it is the part you only install once.