The X-pipe is designed to be used with BBK long tube headers. Part # 1643 / 16430 These BBK short x-pipes are designed from 2-3/4" mandrel bent steel tubing with high flow catalytic converters for maximum exhaust flow. The X-pipe features rear oxygen sensor bungs in the factory location making installation a breeze. Not only is this X-pipe required to finish your long tube header install, it further improves exhaust flow, increasing horsepower, torque and throttle response.