550HP is the Bulk Horsepower or the amount of horsepower the car puts out at the crankshaft. That reading is known as "rear wheel horsepower" to calculate the the bulk horsepower at the engine from where some is lost in the trasmission, air conditioning compressor, pulleys, etc. they take the Rear horsepower x 18%. Thats equals the the 550hp, this is also based or proven on the DYNO test below. So, bottom line, the rear wheel horsepower at 479hp for the 11. Check out the Dyno Test: http://www.youtube.com/watch?v=0GZH0f8J810