The S8 is an Audi A8 saloon fitted with the turbocharged 4.0-litre V8 engine fitted to several other Audis. It comes in a variety of forms, producing anything from 444bhp to 552bhp in different models, but for the S8 Audi has chosen an output of 513bhp.
Despite being made largely of aluminium rather than the heavier and more conventional steel, the S8 has a kerb weight just short of two tonnes. But the engine is still enough to make this a very fast car. Officially, the 0-62mph time is 4.1 seconds, though I have reason to believe that this may be a slightly pessimistic figure. On a full-throttle charge, with the otherwise very quiet engine now bellowing lustily, it doesn't half shift.
That's helped by the standard eight-speed S tronic semi-automatic gearbox, which moves up through the ratios so quickly you can hear the changes more than you feel them. If Audi made a manual version it would certainly be a good deal slower.
Regardless of the above, though, there is never any question that the S8 is at heart a luxurious limousine which happens to have considerable straight-line performance if you're in the mood to use it. The 21-inch wheels and 35-section tyres (an option on the test car - S8s usually run on 20s) don't do the ride quality many favours. But as long as you select Comfort mode in the drive select system a journey over a bumpy road isn't too painful, and the beautifully leather-upholstered seats are very comfortable.
Unlike the A8, the Audi S8 isn't available in long-wheelbase form, so there's not as much room in the back as there might be. However, the car can still transport four large adults - perhaps five at a push - with ease, and those in the back can choose their own level of seat heating and air-conditioning. Behind them there's a 520-litre boot with a hatch which allows you to push a set of skis through into the passenger compartment.
The level of equipment is no lower than you'd expect from a car costing £80,735. The front seats are 22-way adjustable and there's a fine Bose surround-sound audio system onboard too. You also get a parking system with a very useful bird's-eye display which lets you reverse into tight spaces as if you're doing so by remote control from a point high above the car.
The performance is almost secondary to all of this, as is the general driving experience, which is slightly muted. The S8 has been criticised elsewhere for not being exciting to drive. Well, it isn't, but why should it be? It's intended to provide comfortable transport rather than boy-racer thrills, and it does that superbly.
But there's an extra element which most owners will probably never encounter. With Audi's full approval, and indeed encouragement, this test involved competing in a hillclimb event at Shelsley Walsh, where it looked very out of place among all the other cars in its class. Frankly, I didn't think it would perform at all well, but I was very severely mistaken.
Astonishingly, it accelerated up the very steep slope from the start line at slightly more than 1g, and while it couldn't match the class leaders it beat a Subaru Impreza and a Mitsubishi Evo, both heavily modified and running on sticky tyres. It even came within three tenths of a second of vanquishing a Nissan GT-R. It definitely wasn't all about the power, because other cars crossed the finish line 7mph faster than the Audi did. It was partly the start and partly the S8's amazing on-the-limit handling (initial understeer in slow corners soon cancelled out by an easily controllable tail slide when you floor the throttle) that made the result possible.
Onlookers were dumbfounded that a completely standard luxury car could be so competitive. To be honest, so was I. And perhaps the best bit was that for the journey home, the drive select could be switched back in Comfort mode rather than Dynamic as used at Shelsley. This would have made the drive far more serene than it could possibly have been in any other car that recorded a similar time up the hill. You may find it difficult to believe the S8 could be such an effective dual-purpose car, but I can assure you that it is.