McLaren has confirmed the P1's hybrid powertrain will be able to produce 916 HP (674 kW).
The McLaren P1 will be powered by a mid-mounted V8 3.8-liter twin-turbo gasoline engine capable of producing 737 HP (542 kW) at 7,500 rpm and a peak torque of 720 Nm (531 lb-ft) from 4,000 rpm. It will work together with an electric motor generating an additional 179 HP (132 kW) and an instant torque of 260 Nm (192 lb-ft).
The driver will be able to activate the electric motor via the Instant Power Assist System (IPAS) which can be operated by a button mounted on the steering wheel. According to McLaren, this will give the P1 the throttle response of a normally-aspirated engine.
Another button on the steering wheel will turn on the F1-style Drag Reduction System (DRS) which will reduce the amount of drag on the rear wing. The P1's rear wing reduces in angle to lower drag by 23 percent. Deactivating DRS is done by either releasing the button or pressing the brake pedal.
The battery will be installed on the underside of the carbon fiber chassis and will need two hours for a full charge when using a plug-in charger which can be found in the luggage compartment. The 96 kg (211 lbs) battery will allow the McLaren P1 to travel in electric mode for up to 6 miles (9.6 km).
More details are available in the press release section.