Aggressive Throaty Sound. Add the aggressive throaty exhaust note of the Shelby GT500 to your 2011-2014 GT Mustang with a Ford Racing Axle-Back exhaust system. This axle-back features the exact same chambered mufflers found on the mighty Shelby GT500. Stainless Steel Construction. The Ford Racing GT500 Style Axle-Back exhaust system is constructed from 2.75, high quality aluminized 409 Stainless Steel tubing and features 4 polished 304 stainless tips that exit in the stock locations so no modifications are required to the rear bumper cover. 50 State Legal. The Ford Racing GT500 Style Axle-Back is 50 state drive-by noise legal. Application. This Ford Racing GT500 Style Axle-Back exhaust system is designed as a direct bolt on replacement for the 2011-2013+ Coyote 5.0L GT Mustangs, adding great looks and great sound.