BBK High Flow performance X pipes are designed to maximize the horsepower and torque of your 1999-2004 Ford Mustang GT 4.6L 2V and Cobra 4.6L 4V. Every BBK Performance X pipe is designed as a direct replacement for the factory pipe and features larger diameter 16 gauge 2-1/2" CNC mandrel bent stainless steel tubing with a unique BBK center X section for improved exhaust extraction along with high flow catalytic converters to help increase exhaust flow and maximize performance to the rear wheels. These BBK full catted X pipes will install directly to the factory shorty exhaust headers or any aftermarket shorty exhaust and feature factory O2 sensor placement for simple direct installation. A BBK catted X pipe is the best way to really improve your Mustangs exhaust flow over the restrictive factory pipe to increase overall performance plus it will sound great with an additional V8 muscle car growl. Please Note. This BBK product is not legal for use in some states including California: Please check your local emission laws and requirements.