The best cat back exhaust on the market for your FR-S or BRZ. 4 inch Slash Cut Tip Two over-sized 4 inch double wall slash cut exhaust tips add an aggressive look to this impressive system. PERRIN exhaust tips feature double wall construction and will not dis-color with extreme heat. High Tech Muffler This PERRIN Performance muffler has a true 3 inch inlet pipe that carries exhaust into a center chamber before being distributed to, two 2.5 inch exhaust pipes which continue on to the tips.