Road Test: Audi A8 S8 TFSI Quattro 4dr Tip Auto

Even for a firm as niche-obsessed as Audi, something like a full-on A8 RS would be pushing things a bit too far. Happily though, this means it's built an S8: the hottest A8 available, and a car whose performance stats easily outgun even the silky A8 W12. No mean feat.

So the S8 is still a big limo, but with a more heavily defined go-faster bent and V8 shove to make sure you get where you're going on time. And it's not just any V8, but a turbo'd 4.0-litre V8 packing 513bhp and 479lb ft, which means that the near two-tonne A8 manages 0-62mph in just 4.2 seconds. That's an impressive figure - and one that outdoes every other Audi bar the R8 V10 and TT RS Plus - but, in reality, it's nowhere near as startling as the sense of acceleration you get from inside.

The effortless way the S8 puts on speed, and then carries on building it, is almost frightening. It makes the UK's B-roads start to feel like a series of very short straights. A big diesel A8 might match it initially with similar torquey shove, but anything oily will soon run out of revs - and the S8 doesn't suffer from any lack of lung capacity.

But it's not all about pace - despite the fact that it's a large and wanton V8 petrol, there are green points to be scored. This engine features cylinder deactivation, which can shut down four cylinders when you're cruising. Apparently you'll be able to achieve a claimed economy figure of 27.7mpg, which is respectable for such a big car. However, in the real world we never managed north of 21.0mpg... make of that what you will.

Like most Audis, it could do with a plusher ride, and sharper-defined communication through the chassis and steering. Audi has made efforts to liven things up, such as fitting a vectoring sport diff at the rear that pushes the torque to the outside wheel for sprightlier turn-in, but this and the quattro system don't transform the S8 into a B-road hero. It's good, just not that kind of car. Instead, concentrate on the engine, and going fast in a straight line, and you'll love this Audi.

Because it's the first Audi we've driven for a while which has character - it's an Audi you'll care about. It's irrelevant in the UK, where a diesel engine makes sense on so many more levels, but so what? Embrace the lunacy, and embrace the S8.