aFe 3in SS Cat-Back Exhaust | Hummer H2 V8 6.0/6.2L (07-08) (49-44049)Mach Force XP 409 SS Cat Back Exhaust System with Single Rear Exit by aFe. Exhaust System Type: Cat Back. Exhaust Tubing Material: 409 SS. Main Tubing Diameter: 3". Exhaust System Sound: Moderate. 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