On the DynoJet the McLaren 650S put down 569 horsepower and 451 ft-lbs of torque to the wheels. This is 52 horsepower more than the 2013 McLaren MP4-12C they tested on the same dyno earlier.
After some tuning and exhaust work to the 650S, Fabspeed was able to increase the power to 620 horsepower and 509 ft-lbs of torque to the wheels.
Take a look at the video, pictures and dyno graph below.