DEARBORN, Mich., May 2 - The most powerful factory-built Mustang ever just got even more potent. Final certification testing of the Shelby GT500’s 5.4-liter supercharged V-8 shows it will produce 500 horsepower and 480 lb.-ft. of torque – 25 more horsepower than preliminary estimates.

“With 500 hp and the Shelby name, this car is an instant legend,” said Hau Thai-Tang, director, Advanced Product Creation & SVT programs. “This is the most powerful, most capable Mustang ever.”

The Ford Shelby GT500’s supercharged 5.4-liter, 32-valve V-8 is a result of Ford’s experience in developing the modular V-8 and V-10 engine series. The engine is force-fed air via a “Roots-type” supercharger providing 9 pounds per square inch of boost. It borrows the four-valve cylinder heads, piston rings and bearings, from the Ford GT engine.

The 500 hp rating was obtained using the Society of Automotive Engineer’s latest standard and was witnessed by an objective third party. The Shelby GT500’s 5.4-liter supercharged V-8 will be built at Ford’s Romeo Engine Plant in Romeo, Mich. Pricing will be announced closer to launch.

The right to purchase the first 2007 Ford Shelby GT500 was auctioned for $600,000, with the proceeds benefiting the Carroll Shelby Children’s Foundation. The 2007 Ford Shelby GT500 goes on sale this summer.