Road Test: Audi RS6 4.0T FSI V8 Bi-Turbo RS6 Quattro 5dr Tip Auto

The Audi RS engineering department has been infiltrated by vegans. This will probably be your first thought when scanning the specs of the new RS6 Avant. Fewer cylinders. Less power. Greater efficiency. Lower CO2 and more mpg. With start/stop and cylinder-deactivation as standard, it also looks like it spends most of the time it is doing something trying to switch itself off. But look again. Less weight. More torque. More speed. Torque-vectoring. Electronic stability control that can be completely deactivated. A sports exhaust that sounds like a tiny army having a small but important war in the boot, and the kind of point-to-point performance that bruises atmosphere. Aha. Seems like the RS department's loons are alive and well - they've just learned to veneer their insanity with a thin film of environmental respectability.

So this is the new RS6 Avant, and the recipe remains pretty much the same as before. A big-engined version of the A6 Avant, all-wheel drive, auto 'box. But the execution is different. Cleverer. A 4.0-litre V8 instead of a 5.0-litre V10. Better balance. More thoughtful deployment of resources. Now, the previous bi-turbo V10 was an excellent express train for mauling Das Autobahn, but tended towards the bloodless when attempting a corner (it required extreme conditions to really show you what it was capable of), and fuelling it was like tipping buckets of unleaded down a car-shaped storm drain. So this version attempts to deal with some of those issues.

First up, if you address the upward spiral of mass, you'll get a car that handles with more fluency and goes faster for less energy output, which means you spend less time setting fire to your monthly wages in a neat little engine-shaped bonfire. The RS6 therefore gets lots of lightweight aluminium in its make-up - about 20 per cent - including the front wings, the doors, the bonnet and the bootlid. But they're just the bits you can see. Inside, the transverse strut in the boot floor is ally, as are the castings for the front strut domes and the crossmembers behind the front and rear bumpers. The rest of the body is good old-fashioned high-tensile steel, with some exotics thrown into the mix - the steering wheel is made of magnesium - and every single thing has been pared to try to make the porky estate into something a little more lithe. I particularly like the facts that the electrical system's wires have the smallest possible cross section and the sound-deadening materials have been chosen specifically because of their low weight. I like my engineers incredibly anally retentive.

It's no featherweight, but the result is nearly a 100kg weight reduction in a car with more kit, which also complies with more EU crash and pedestrian rules than ever before. This is good. So it's got two fewer cylinders and 28bhp less than the old version, but it's also got 37lb ft more torque and is faster in every respect, including a 0-62mph time of 3.9 seconds and 189mph top speed if you option the correct limiter. There's a rumour that the car scrapes 200mph totally derestricted, but requires its tyres to be pumped uncomfortably hard to cope, and 190-ish was decreed to be sufficient for most needs - which is hard to argue with.

Of course, adding lightness is good for efficiency, and the new RS6 is a decent chunk more fuel-efficient than the old version - up to 30 per cent. Part of that is down to clever aircon and thermal management, but there's also COD (Cylinder On Demand) tech in the engine, which we've seen before on various cars. This simply shuts down half the cylinders when running a light throttle. In the case of the RS6, if you're using under 3,500rpm on a constant load, then the car drops cylinders 2, 3, 5 and 8 out of service. Doing so generally reduces fuel consumption by about five per cent on the usual combined cycle, or as much as 12 per cent at a steady 62mph cruise. Which isn't to be sniffed at, especially as a twin-turbo V8 isn't likely to be particularly drink-shy if you decide to boot it. Also, and more importantly, you just don't notice. In fact, it only becomes obvious if you look for the little tell-tale light on the dash - as soon as you increase the load, you get all eight cylinders reanimated and ready for action.

Hilariously, the RS6 uses active engine mounts to cancel out extra vibration when running as a V4. There's a lot of important-sounding science here, including some stuff about ignition only occurring every 180 degrees of crank angle, producing higher rotational oscillations. This translates more understandably as an increasingly wobbly engine when the cylinder shut-off is engaged. The best bit is that the RS6 then uses ‘electromagnetic oscillation coil actuators that induce phase-offset counter oscillations' to cancel out the vibration. Once you've sieved that little lot through engineering Babel, it turns out that, basically, the active engine mounts and a couple of other bits zig as the V4-spec engine zags, and keep everything running smoothly.

Of course, we've seen the 4.0-litre V8 before, notably in the S6, S7 and S8, the forthcoming RS7 and the Bentley Continental V8. And it's a goodie. A pair of turbos perch within the banks of the vee (they sit just under the V8 TFSI badge on the engine cover) like a pair of hibernating snails. There's an air-water cooler nestled next to them, in a layout that shortens the relevant pipework to a minimum, equating to less lag before the turbos start to fatten the torque curve. And a very pious pair of domesticated tornados these two are, absolutely dedicated to cramming as much air as they can into a possibly slightly surprised-looking octet of cylinders.

This is where the RS6 starts to get interesting, because the way it makes torque is the entirety of the reason it's possibly one of the best real-world, point-to-point blasters on the planet. From 1,750rpm - about twice idle - the RS6 produces maximum torque of 516lb ft - which is similar to a big turbodiesel. So far, so useful. The big news is that the RS6 continues to produce maximum torque all the way to 5,500rpm, the point where most diesels have run out of lung, at which point it starts to produce its maximum power of 552bhp at 5,600rpm, which it makes until the 6,600rpm red line.

The performance is not what you'd call ambiguous. A standing start will bring a little squirm from the back wheels as they lose traction from the standard 40/60, front/rear torque split, but, after that, the clever centre differential can punt torque up to 70 per cent forward or 85 per cent rearwards depending on which end is slipping. Which means the car has a general tendency to grip, go and make you do an uncanny impersonation of someone trying to inhale a steering wheel. The official figures quote a blink under four seconds to 62mph, and it feels eminently repeatable, all without any need for fancy launch control; just brake with left foot, rev with right and then lift the former and drop the latter.

Through the gears, it simply has no peaks or troughs. Which might sound a bit boring, until you're sat behind it running through an emotional rainbow that breaks down into roughly one-third focus, one-third excitement and 40 per cent terror. On a small B-road, the RS6 is still a big car, and the rapidity with which it can inject itself into the view means that bit between here and there becomes an intense experience. Full throttle brings the sound of a month's worth of breathable oxygen molecules genocided in those turbos. When the exhaust flap opens up with an audible thunk at just under 3,000rpm, the car sounds like an exploding tuba. In a good way. And the banging and popping on the overrun is gloriously addictive. The car we had came equipped with the optional sports exhaust, and all RS6 owners ought to be required by law to have it. It never drones, sounds incredible and is worth whatever they decide to charge for it - even if more than the actual car.

The gearbox is actually a standard A6 ZF eight-speed, albeit with punchier shift characteristics, the first six gears for play, the last two making a decent fist of low-rpm cruising. It's just about perfect. The fact that it's a torque-converter rather than a DSG means that it negates the initial and in-town hesitancy that DSGs sometimes exhibit, making for a relaxing car to simply bumble about in. It's also snappy enough in the up- and downchanges to satisfy, even though it's probably giving away a few microseconds to the fastest gearboxes on the market.

The best bit? The RS6 now handles properly. The engine is short - only 497mm - compared with the old V10, and some clever positioning of bits means that the RS6 now has a much-improved balance front to rear. And it shows. It still leads slightly with the nose, but throw in the active diffs and general trickery, and this is a big estate that's proper fun - it'll even slide a bit, though you need space and a smaller imagination than I possess to do it much on a public road.

All that before we've even thought about how it looks - which you can make your own mind up about. I like the basically Schwarzenegger-spec A6. Blistered arches, jutting nose, rear spoiler, 20-inch wheels as standard with 21s as an option. It looks hard - especially with some of the optional matte paint schemes and dark wheels. So it's not as much of a street-sleeper as it used to be, but neither is it completely bonkers. It even rides acceptably on the 21-inch wheels - in Comfort mode. I tried Dynamic and didn't need to blow my nose for two days, so best save that for the track. In summary? It's the most amusing car that Audi makes - including the R8 - for sheer wilful silliness. It might not be perfect, and I'd really like to try it on a UK backroad, but so far, TopGear mag likes the RS6. A lot.