To get back to the full beans for a second stint, we come in to hook the car up to its charger - a humming three-phase 20kW contraption with a cable like a ship hawser that’ll fill the battery in just 40 minutes. A good time to talk to Paul Newsome, project head, about why they selected the balance of engine power, electric power and battery size. At one extreme, couldn’t they have just stuffed the V8 in there and forgotten the rest? “I can confirm the V8 won’t fit,” says Newsome before the question has fully left my lips. But anyway, a modern supercar needs sensible economy. Not the ridiculously artificial economy of the official test and its CO2 result (these ignore energy taken from the grid and the CO2 that stems from it), but enough economy to give decent driving range. To get that, some engine downsizing was important. But that tends to mean a combination of low torque and/or turbo lag. So it’s sensible to add electric motors, not just because that gives you hybrid-fuel-economy benefits, but for their instant response, amenability to high-finesse traction-control systems and four-wheel-drive ability. OK, so how much electric power to give the system?
Newsome says they modelled a whole range of balances of electric to piston power, with various battery sizes to boot. He decided on 500bhp from the engine, so that, even after using up the batteries in full-fat mode, there’d still be enough combustion power for a sustained 190mph top speed (“We thought about where there were roads in the world that you could use all the performance and for how far”). But the batteries and motors are something special, and they give the system the flexibility and power it has. First, the little axial-flux motors, which can produce several times more power for their weight than a conventional motor, and have a wider operating range too. They’re each just 22kg for their 200bhp and 300lb ft, and not much bigger than a round washing-up bowl. So the car could use lots of electric power. Second, they wanted to use a high voltage because it’s more efficient, settling on 600V. As the voltage is proportional to the number of cells, that pointed to a big battery. They got a 19kWh unit, mostly packed down the central spine of the car. It uses the same power management and cell chemistry as a Williams F1 battery, and so its power density is about halfway between existing road cars’ and a grand prix car’s. Having got the battery they needed for the power they wanted, it turned out the electric-only range was just what they were wanting too.