Anyone who prizes the quality of stealth will see great appeal in the new Audi S6. Indications that this isn't merely a regular A6 with big wheels are spectacularly subtle considering the engineering feat the S6 conceals. The clues amount to little more than vertical spars for the deep front grille, four small tailpipes and a couple of extra badges beneath the side repeaters. But those little badges read 'V10' because, like the recently launched S8, the S6 has a 5.2-litre version of the Lamborghini Gallardo's V10 in its nose. Why so discreet, then? Partly because within the year there will be a full-on, twin-turbo RS6 with over 500bhp, designed to vanquish the BMW M5. Still, the S6 has a healthy 429bhp, almost as much as the last RS6, and will cost £55,330 (£1270 more for the Avant) when UK deliveries begin in July. That price is not a lot more than the £50K for the RS4, which has marginally less power - 414bhp from its high-revving V8 - and there's arguably more kudos to driving a fast Audi with the Gallardo engine under its bonnet. That's not quite what you're getting, though. Audi describes the 5.2-litre V10 as a 'derivative' of the Lamborghini's V10, and in fact the 5.2 shares very few components with the 5-litre Lamborghini unit, the only significant shared parts being the drivetrain for the four camshafts. The reason is that the Audi V10s are built at the same factory as every other Audi engine, which, for economies of scale, has been configured to produce engines with a common 90mm bore spacing. The bore spacing of the Gallardo engine is 88mm. This is how the Audi V10 ends up with a different cylinder block, a new crankshaft, different pistons and new camshafts, while the more restricted engine bay, plus Audi's desire to give the engine its FSI direct injection, result in bespoke induction and exhaust systems and a new sump. It's a new engine, then, and a marvel of packaging. Lift the S6's bonnet, walk to one side and stand level with the centre cap of a front wheel. From here you can see that the whole of the V10 is ahead of the front axle line. Having 220kg of engine hanging out beyond the front axle isn't the best starting point for a dynamic drive. The problem with adding more cylinders isn't simply the weight, it's that the further forward the weight is, the greater its effect on weight distribution. Yet the S6 doesn't feel nose-heavy. Its quattro drivetrain uses the more sporting 40:60 front:rear torque split introduced by the RS4, and the car feels taut and together, much as the RS4 does. The ride is firm at town speeds and there's a keenness about the way the S6 responds to steering and throttle inputs that makes it feel alert, smaller than it is. At idle, the 10-cylinder unit is softly spoken, and although only a six-speed auto is available, the S6 steps off very keenly. A hefty kerbweight of 1920kg is well disguised at low speeds by almost 400lb ft of torque, delivered between 3000 and 4000rpm. Much of the time you wouldn't know there was a V10 under the bonnet. On the overrun there's a rolling- thunder rumble from the tailpipes, but overall the M5's V10 is more stimulating, feeling more urgent and sounding more enthusiastic. Mind, Audi pitches the S6 as a luxury car with sports car performance, which is about right. At speed or over rippled, lolloping roads, the damping reveals itself to be not as expertly controlled as the truly sporting RS4's, and here perhaps the mass of the V10 has an effect too. Dynamically this is a neat car, but your (and the car's) enthusiasm for pressing on stops short of the level inspired by the RS4. If it's a bigger RS4 you're after, best wait for the RS6. If it's quiet speed you're after, the beautifully built, refined S6 fits the bill.
|Engine||V10, 5204cc, 40v|
|Max power||429bhp @ 6800rpm|
|Max torque||398lb ft @ 3000-4000rpm|
|Top speed||155mph (limited)|