Normally, when someone builds a prodigiously powerful V8 diesel, they take it to a boatyard and bolt it to the back of a powerboat. It's the right and sensible thing to do.

But in this case there was clearly an embarrassing mix-up, possibly involving the word 'flagship'.

You see when Audi's finest engineers created a 321bhp engine with enough torque to lug an oil rig off its moorings, instead of installing it in some kind of high-performance motor launch, some chump got the wrong idea and dropped it into a high-end executive car by mistake.

Red faces all round. And that, car fans, is the true story of how Audi's A8 4.2 TDI came to be the most powerful diesel production car in the world. Only, of course, it isn't. It happened because Audi wanted to be the first German manufacturer to bring an überdiesel saloon to the diesel-hungry British market.

And, for now, it is the most powerful oil-burner around. But although Audi's V8 boasts more horses than the 309bhp V10 diesel powering VW's Phaeton, it can't match the five-litre V10's 553lb ft of torque. That's roughly enough twisting force to pull a fully-grown Douglas Fir out by the roots.

But perhaps that's splitting hairs. Or snapping treetrunks. The fact is, Audi's daddy of all diesels' 321bhp of power is 50 horses up on the four-litre diesel it replaces and its peak torque of 479lb ft arrives in a wave from 1,600 and 3,500rpm.

I'm not sure anyone really needs that that much torque, after all, you don't see many A8s pulling caravans come the August bank holiday.

The other traditional advantage of diesel is, of course, fuel economy. And the 4.2 scores over the outgoing 4.0 here too, with a claimed 30mpg combined figure, which contributes to the Audi's phenomenal range. Driven with a light right foot, the A8 can, according to Audi, go for 590 miles without stopping. What a shame then that so many A8s are driven by silver-haired admirals of industry whose bladders long ago lost the ability to match such an epic, long-distance voyage.

The A8's equipment has received a refit too; SE trim now comes as standard and sportier wheels and suspension can be specified, as can a Bang & Olufsen sound system.

Audi likes to think of its new A8 4.2 TDI as a 'diesel supercar'. Hmm. That's pushing the boat out a little too far. But only just.

Richard Fleury

Back to Audi A8 Overview