Milltek Sport cat-back exhausts for the B8 S4 are constructed from stainless steel, mandrel bent, 2.37" (60.30mm) tubing. The ultimate sport precision tuned exhaust system. A perfect fit for your 3.0T Audi, back-pressure will be reduced by at least 30% from the stock Exhaust. By reducing back pressure you will see an increase in horsepower, torque, torque, fuel economy and throttle response. This exhaust system features a center resonator to provide a more refined exhaust tone when compared to the non-resonated systems. This Milltek exhaust system is a complete bolt-on system and requires no cutting or welding to install.