Basically an MP4-12C powertrain (3.8 TT V8, 7-speed dual-clutch) with an electric motor added, also putting power down through the rear wheels. ICE is 727HP, electric motor is 176HP, so power under electric boost is 903HP.
http://inhabitat.com/mclaren-set-to-unveil-903-horsepower-p1-hybrid-supercar-at-the-geneva-motor-show/
Odd that they didn't hook up the electric motors to the front wheels like the Porsche 918, near-4-digit horsepower won't be easy to control through the rear wheels alone.
