During the muscle car days of yore, automakers would deliberately sandbag (or in some cases, inflate) their own horsepower numbers in an attempt to throw off insurance companies. This was a time before dynos were in widespread use, and most consumers were never the wiser. These days though, many consumers drive their cars from the dealership to the dyno, wanting to see exactly how much power gets to the ground.

With the first 2013 Shelby GT500’s just hitting dealerships, the new owners are wasting no time. Mustang 5.0 Magazine was on hand when a 2013 Shelby GT500 hit a mobile chassis dyno, and you won’t believe this. The 2013 Shelby GT500 put 609 horsepower down at the wheels, which may mean that Ford has seriously underrated its own monster.

When Ford first announced the 2013 GT500, it put the numbers at 650 horsepower and 600 ft-lbs of torque. Then the official ratings came through at an even higher 662 horsepower and 631 ft-lbs of torque. This is flywheel horsepower; as drivetrain losses usually suck up about 15-20% of the power before it makes it to the wheels.

On the dyno, this 2013 Shelby GT500 put down 609 rear-wheel horsepower. Without knowing the ambient temperature or elevation, it’s hard to tell how indicative these numbers really are of true horsepower numbers. But if they’re even close, it means that Ford seriously underrated the 2013 Shelby. Figuring for 15% drivetrain loss, a rating of 609 rear-wheel horsepower would mean flywheel horsepower is close to 700 horsepower.

Yes you read that right…the 2013 Shelby GT500 makes 700 horsepower. Simply put…slam.