Valvetronic Design Mercedes C63 AMG W204 Valved Sport Exhaust SystemThe M156 6. 2 Liter V8 is one of the all time great engines. With an insane bark, this engine is the reason so many people choose the C63 over the equivalent M3. trouble is when you are running long tube headers or other exhaust modifications the car is constantly loud even when running the stock rear muffler and resonator combination. With this valved system, you can have both that killer sound when you want, and the ability to terminate the sound at