BBK 1637 2-3/4" High Flow Performance Short Mid X Pipe With High Flow Catalytic Converters For Ford Mustang  (Required For Use With BBK Long Tube Exhaust Headers) BBK is your Number One Aftermarket Performance Exhaust Brand in the USA - American Designed and Built BBK Hi Flow Short Mid Pipes are Required to Complete the Installation of BBK Full Length Headers to the Cat Back Exhaust System Built with CNC Mandrel Bent Tubing for Increased Horespower, Torque and Performance Available in H or X Pipe Configurations with High Flow Catalytic Converters or Off Road Race Only Versions 2-3/4" Inch Short Mid X Pipe with High Flow Catalytic Converters - Fits BBK Performance 2005-2010 Ford Mustang GT Full Length Headers Part Numbers 1641,16411