MagnaFlow SYS C/B 04-05 Audi A4/S4 4.2L DSRThe MagnaFlow 2004 2006 Audi S4 Sport Series Cat Back Performance Exhaust System 16586 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