Armytrix Stainless Steel Valvetronic Cat Back Exhaust System (OE Valve Control)Enhance your Audi RS4 RS5 (B9) Avant Sportback by adding the ARMYTRIX Valvetronic Stainless Steel Exhaust System. This system will increase power, reduce weight, and improve sound. This precision made performance system delivers more power, especially in the low and mid rev range, the effect on the sound is significant, adding a deep resonant sporty sound, but at the same time neutralizes the annoying frequencies in the most critical rpm range.