V6 engine , replacing the 3.8 L pushrod V6. The Mustang GT features a more rugged Tremec TR-3650 transmission with an aluminum 300 hp (224 kW) 4.6 L 3-valve Modular V8 with variable camshaft timing . 2007's Shelby GT, based on the standard GT model, is modified by Carroll Shelby International to produce 319 hp (238 kW)