After months of teasers and speculation, McLaren has finally released details of the drivetrain that will power its new P1 - and in this case the term 'supercar' is justified.
The P1's combination of a mid-mounted 3.8-litre twin-turbo V8 petrol engine and a highly effective electric motor gives a combined output of 675kW and 900Nm, for instantaneous throttle response across the rev range, more like that of a big naturally aspirated engine.
A camouflaged P1 prototype in testing.
The petrol engine is a new version of the M838T unit found in the MP4-12C, upgraded to optimise cooling and durability under the higher loads, and using a special block that also houses the electric motor. McLaren quotes 542kW at 7500rpm and 720Nm from 4000rpm.
PEAK TORQUE FROM STANDSTILL
The lightweight electric motor, developed by McLaren Electronics specially for the P1, is rated at 131kW and, like all electric motors, produces its peak torque of 260Nm from standstill, for instant throttle response at low revs, allowing the engine techs to tune the V8 more for top end.
The electric motor is mounted directly on the engine, and all the drive is channelled through the dual-clutch seven-speed gearbox for seamless power delivery to the rear wheels.
The electric motor also provides lightning-fast upshifts by reversing the connections to the stator windings for a few milliseconds just as the clutches change over, creating a momentary negative torque that makes the engine revs drop as quickly as possible to the correct speed for the upshift.
Not only that, but as soon as you take your foot off the loud pedal the electric motor switches over to generator mode, slowing the car down and turning waste energy into amps for the battery.
The P1 can be driven in a variety of modes, powered by the engine and electric motor together, or by the electric motor on its own in low-emission zones or for near-silent running in residential areas.
Driven with finesse the P1 can travel more than 10km on pure electric power - enough for most city journeys - and when the battery goes flat the petrol engine will automatically start to keep the car going and charge the battery.
The power available from the petrol engine and electric motor also benefits further from two steering wheel-mounted buttons which activate the drag reduction system and the instant power assist System.
The drag reduction system is similar to that employed on Formula 1 cars; speed is increased by reducing the drag on the rear wing. Where the MP4-28 has a moveable flap on the rear wing, the P1 flattens the angle of the whole wing by 23 percent - until the button is released or the driver touches the brake pedal; then the wing instantly returns to the standard angle for maximum grip.
131KW EXTRA - INSTANTLY
Instant power assist provides extra acceleration by simply shorting the battery straight through the electric motor, giving the driver an instant 131kW power boost.
It's made possible by a special lightweight battery pack with class-leading power density and an innovative 'intelligent' cooling system. The battery weighs only 96kg and it's mounted straight onto the underbody of the carbon-fibre monocage chassis, which seals the battery into the car and saves the extra weight of brackets and casings.
Shorting the battery out, however, produces a lot of heat, which can do nasty things to cell performance and reliability, so the coolant flow is balanced across the entire pack to maintain each cell at the same temperature.
In addition to the engine using the electric motor as a generator to charge the battery, the P1 comes with a plug-in charger that can recharge it from flat in only two hours. The charger can be docked in the luggage compartment, but it's quite heavy, so it can be removed to save weight and stored in the garage - or the pits.