XR Style Exhaust System Fits: 2:2 RACE SYST H-D XLH883-1200 "04-11, SS These 4” diameter disc-based megaphone series are our signature muffler and provide 8-10% horsepower gains. The classic megaphone design allows the exhaust gas to expand which increases power while the discs let you control just how much flow you want. Optional open end caps for closed course competition are also available. Available as slip-ons, 2:1, 2:2 and 2:2 XR Style systems – the 2:2 XR Style system provides a bolt-on 20% horsepower gain. Twelve - 4” discs are included with slip-ons and the 2:1. Twenty-four - 4” discs are included with the 2:2 systems – that’s 12 discs per muffler. Add 4” discs to increase horsepower, exhaust tone and flow. Remove 4” discs to reduce sound and increase low-end-torque.