APR Valved Cat Back Exhaust SystemThe APR Catback Exhaust System for the Audi B9 S4 and S5 is a complete high performance exhaust solution, running the full length of the vehicle from the catalyst back. Inspired by the larger centre pipe design found on higher output RS4 and RS5 models, this system is engineered to deliver increased performance, an aggressive exhaust note, and a striking visual upgrade. Designed and manufactured using premium materials and advanced production