Surprise! It's the diesel R8

We knew Audi was planning something big in Detroit, and here is it: the world's first diesel supercar.

This is the Audi R8 V12 TDi, and although it's being billed as a concept, it should be on the road within a couple of years.

Tearing massive holes in the road, quite possibly. The R8 V12 isn't a cooled-down version of Top Gear's Car of Year: in fact, the diesel version is billed as faster, more powerful and - of course - far more torquey than its petrol brother.

A few raw figures for you. The R8 TDi gets a 5.9-litre V12 twin-turbo diesel with 493bhp and, more scarily, a massive 738lb ft of torque. That'll shove the R8 to 62mph in 4.2 seconds - nearly a half-second quicker than the petrol version - and on to a top speed 'well over 186mph', according to Audi.

Awesome performance, in other words. But it won't come at the expense of economy: The R8 V12 returns 23mpg - just 4mpg less than the V6 TT - and although there's no word on emissions, Audi says it'll meet the 2014 Euro 6 regulations.

All of which sounds like an intoxicating combination, leaving us with just one worry: weight. Audi doesn't quote how much heavier the TDi unit is than the petrol V8, but too much extra weight could play havoc with the R8's delicate, wieldy handling.

However, Audi has managed to shave some weight from the diesel block by using stronger cast iron, allowing for thinner crankcase walls, which reduces weight by some 15 per cent.

Although the bodyshell of the R8 V12 is taken straight from the petrol version, the diesel-burner does get a few cosmetic enhancements. There's a glass roof with a NACA air duct in the middle, as well a new single-piece front bumper and bigger air intakes.

Inside the cabin, there's a bit of extra carbon fibre and, you'll notice, a manual gearbox. Word is that all the diesel torque would simply devour the DSG ?box, so a six-speed shifter it is - good news, because that's the ?box we liked on the petrol R8 anyhow.

We won't see the diesel R8 on the road until after the new Lamborghini Gallardo - and you'll see a V10 petrol version of the R8 beforehand, too. The V12 TDi could be the most tempting of the bunch, though - if the Audi engineers can make it handle like the petrol version. Here's hoping.