Added to AFE 5" Straight Pipe at 7.3. Didn't mind the straight whistle sound, but lugging the 5 Series around town was too much. Place this muffler in place of the muffler removal tube. Significant reduction in idle noise and acceleration noise. Haven't towed it yet but very happy so far. Note: Make sure to install according to MBRP installation recommendations regarding flow direction. In the installation instructions there is a picture showing the internal structure of the muffler and the direction of the exhaust gas flow.