Why 2.75 Inch piping diameter? After much research, calculations, testing and development we found that based on the 4.2L 32v V8 engine's demands, 2.75 Inch piping diameter is the optimal size. With a 2.5 inch exhaust you end up choking off the RS4's free spinning and high-revving V8. We have also found with a 2.75 inch downpipes that torque is not sacrificed for power gains in the top end of the RPM band.

Not for sale or use in the state of California on any pollution-controlled vehicle as per the California Air Resources Board.