XP Series™ 409 SS Cat-Back Exhaust System with Split Rear Exit (S7018409) by MBRP®. Exhaust System Type: Cat-Back. Exhaust Tubing Material: 409 SS. Main Tubing Diameter: 3". Exhaust System Sound: Moderate. The XP series exhausts from MBRP is for the no-compromise enthusiast who insists on a rugged system that can take whatever the road throws at it and last. Constructed entirely of corrosion-resistant T409 stainless steel, this system will show some light surface discoloration after a while, but will never corrode through.