Mach Force XP 304 SS Cat-Back Exhaust System with Tip (49-36313) by aFe. Exhaust Type: Cat-Back. Tubing Diameter: 2.5in. Get increased exhaust flow, more horsepower and torque, improved performance and lower exhaust gas temperatures with the aFe Mach Force XP Cat-Back Exhaust System. aFe dyno tests every system for maximum gains, and constructs them from mandrel-bent stainless steel for maximum flow and long-lasting durability. This system begins at the Cat (Catalytic Converter).