I think he's doing it with around 1,300 horse power! Listen to the engine toward the middle. He's just gently revving it around the bottom of the power band and still keeping them spinning!!!
You know your engines been working when the heat of the exhaust still ignites the air at the end of a 10' exhaust!
They say the 1,000HP Bugatti Veyron engine actually produces over 3,000HP worth of energy if you could harness the heat produced by the engine at full throttle...