McLaren spills 403km/h Speedtail's secrets

McLaren has published full details including previously unreleased technical info on the advanced 773kW hybrid V8 that will power the McLaren Speedtail to its 403km/h top speed.

Until now, only its power output had been revealed, but the Woking-based supercar-maker has finally unveiled what lurks beneath the Speedtail's streamlined body.

The safe money was always that the Speedtail's electrified powertrain would centre around the car-maker's twin-turbocharged 4.0-litre V8 and, indeed, the powerful bent-eight makes an appearance -- but it has been heavily modified to produce more power.

In comes a lighter air intake system, a redesigned cylinder-head that offers better cooling and a set of new pistons.

Alone, the changes all help it to contribute a heroic 557kW and 800Nm, but without electrical assistance it would fall short of achieving the Speedtail's towering top speed.

Making up the deficit is an electric motor that's said to be inspired by a Formula E racer's powertrain, and produces as much as 230kW.

Feeding it power is a lightweight, compact 1.6kWh battery pack that's said to have a power density four times that of the McLaren P1 and the best power-to-weight ratio of any 'high-voltage battery available today', McLaren claims.

As well as being state-of-the-art, the new batteries are said to be immersed in a lightweight, electrically insulative oil which quickly transfers heat away from the cells, allowing it to rapidly deploy and recharge without the overheating that kills performance.

McLaren says the result is a hypercar that can muster a total of 773kW and 1150Nm of torque -- enough to launch the Speedtail from rest to 300km/h in just 13 seconds and on to its maximum 403km/h top speed.

To conclusively prove the 403km/h top whack, McLaren engineers repeatedly achieved the top speed more than 30 times in consecutive runs on a Florida runway back in December last year.

Now officially the fastest McLaren ever made, the 403km/h Speedtail finally usurps the original McLaren F1 that, back in 1998, had its rev-limiter in sixth gear removed to clock 386km/h.