How does a Jaguar engine sound at 10,000rpm? Click on the sound file below to find out. With any normal Jag, it would be the sound of mechanical catastrophe. What you have here, instead, is a hard-edged howl of performance that takes you straight back to the four-pot turbo F1 cars of the 1980s.
The engine of the C-X75 hypercar is safe to this dizzying figure. Top Gear heard, and saw, the prototype engine safely doing this today, its turbo glowing red-hot (below). It makes 500bhp from 1.6 litres and has a supercharger and a turbo.
OK, it's not the jet turbines of the concept car (Jag says they're not ready for prime-time quite yet), but it's still a pretty out-there engine. But frankly that's just one of many amazing facts about this car.
Another is that, if it's given the final nod for production in 2014, it will cost a million quid.
It's four-wheel-drive, with the rear wheels driven by that engine, plus an electric motor, both channelled through a lightweight seven-speed box. The front wheels have their own single-speed electric drive.
The total power of those electric motors is around 400bhp. That's in addition to the petrol engine.
The battery is capable of delivering a quarter of a megawatt for a short full-bore burst.
All of which means performance that's smacking of gob. Here are the numbers: 0-60mph in less than three seconds, and 0-100mph in less than six. Top speed is 200mph-plus.
Oh and it's a plug-in hybrid, which means the option of electric-only drive. In that mode it'll do 40-odd miles if you're gentle. And unlike any other plug-in (even the Porsche 918), it still has sports-car acceleration in electric-only mode, getting from 0-60mph in about six seconds.
At the moment the C-X75 is not finally signed off for production. Jaguar people are super-keen, and they're building five prototypes so there's big money being invested. But Jaguar Land Rover engineering boss Bob Joyce says they'll have to get it to smoothly deliver its performance, melding all three powerplants, before they'll sign it off.
And then they'll build 200 cars, starting from 2014, at (gulp) £700-900,000 apiece. Plus VAT.
The team developing the car is based at Williams GP Engineering. Williams is contributing expertise on aero (it's got moving spoilers) and on composites (the whole body and tub is carbonfibre). But most of all, Williams' knowledge of KERS is coming in useful.
Jaguar says the electric motors are three times as powerful for their size and weight as conventional motors. They're also capable of producing torque efficiently through a far higher speed range than normal e-motors. All of which is possible, oh electric-motor-spods of the interweb, because they are of the axial-flux type.
The rear motor is geared along with the engine through the automated manual transmission. The gearbox itself is about 100kg lighter than a twin-clutch box, Jaguar says. It's the same argument Pagani uses for the Huayra. And here, the e-motors can be used to smooth-out the gearchanges. Given that the batteries are 200kg, Jaguar needs to save weight wherever it can.
At the moment, the prototype has 11 radiators. They cool the engine water (x2), the engine oil, the motors, the electronics, the battery, the cabin, the transmission and the water for the intercoolers. Numbers 10 and 11 are the two intercoolers themselves. The engineers are trying to combine some of those rads, so they can get rid of one or two. This will make room for the one amenity the car currently lacks - a boot.
Another huge challenge is to get the car to sound exciting in electric mode. The team doesn't want to use simple engine-sound mimicry, but they want something that adds to the drama and sense of performance. Probably not the Muse Olympic anthem then.
On the other hand, there's a sport mode, which keeps the engine running all the time.
What about comparisons with the Porsche 918, you ask. Well the Porsche, too, has 4WD, a motor at the front and another at the back, and a seven-speed box (but a twin-clutch) for the back wheels. But the Jag has more electric motor power than the Porsche, and about three times the battery capacity. It's a more electric-biased car. And where the Porsche has a naturally aspirated 700bhp V8, the Jag has this remarkable little 500bhp four.
Come 2014, it's going to be hard to choose. Mind you, most people in this wealth bracket will probably buy both.
No-one will turn down the Jag because of its looks. We're promised that, bar a few extra vents for all those radiators, it will be just like the concept car.