SCT Performance Tuners - 07-11 Mustang Shelby GT500 Custom SCT X3 Flasher/Tuner The Mustang Shelby GT500 is the most powerful production Mustang Ford has ever produced. The GT500 has an amazing amount of potential waiting to be unlocked. With a safe 93 octane tune we picked up 60RWHP and 40RWTQ! Stock the GT500 will dyno at 420-440RWHP and 440RWTQ SAE corrected on an industry standard Dynojet. With a 15% drivetrain loss that is 500-520HP at the crank. We have spent countless hours perfecting our GT500 tunes on our own test vehicle and have used them on hundreds of customers cars.