The MagnaFlow 2004-2006 Audi S4 Sport Series Cat-Back Performance Exhaust System enhances your 4.2L 2004-2006 Audi S4 with an aggressive character that is sure to help you stand out from the other Audi S4 you encounter on the street. With its 2.5in. diameter fast-flowing mandrel bent main piping that passes through 4 Straight-Through mufflers before ending in a Dual Split Rear exit with 4in. Polished Welded-On Double Wall Angle Cut Rolled Edge tips, this dyno-proven Audi S4 exhaust system refuses to be ignored. As such, 16586 is tuned to produce our powerful, resonant signature exhaust note at Aggressive exterior and Moderate interior sound levels, so please check to ensure compliance with local noise regulations. The system's cat-back design replaces all your import's stock exhaust components from the catalytic converter on back. Extensive 3D scanning and CNC precision robotic manufacturing techniques are used to ensure that your exhaust system fits perfectly with just a simple do-it-yourself installation process. The durable, corrosion resistant stainless steel construction of 16586 is backed by MagnaFlow's limited lifetime warranty.