What is it?
The world’s first drive of Audi’s new V8, complete with ‘cylinder deactivation’ technology, which will debut in the production version of the Audi S8 later this year.
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The one you’re looking at here is a prototype, but it’s good enough to get a strong impression of how this engine will work on the road – even if we didn’t get a real opportunity to feel how the S8 will be as an overall proposition.
This is an important engine for Audi – and Bentley. Versions of it will also find their way into the S6, the S6 Avant, the S7 and the Bentley Continental GT, slashing the fuel consumption of all of them.
Where to start? Audi has taken a leaf out of BMW’s book by firing the exhaust gases out into the middle of the 90-degree V8, where two twin-scroll turbos are nestling to reclaim their energy. There’s direct fuel injection and variable valve timing as you’d expect from a top-spec Audi, but the really clever bit is the way this V8 can turn itself into a V4.
When it doesn’t need full power the Audi deactivates cylinders 2, 3, 5 and 8. That can only happen when the engine is producing less than 185lb ft of torque, the car is in at least third gear and there’s between 1000 and 3500rpm showing on the tacho. If all the boxes are ticked, sleeves on the camshafts slide electro-mechanically to move ‘zero lift’ lobes next to the sleepy cylinders. The system can re-fire the idle cylinders in just 0.3 seconds.
Audi counteracts the potential for noise and vibration from the now-V4 engine with clever active engine mounts and ‘Noise Control’, which has four microphones in the cabin searching for unwanted sounds and harmonics, which are then cancelled out by playing the ‘inverse’ waveform.
What’s it like to drive?
Silky. It really doesn’t sound like a V4 half the time. For a start, the gorgeous, bass-heavy V8 rumble is unaffected in first and second gears. You only really know that four cylinders have cut out when the digital efficiency bar between the speedo and the tacho turns green to show that you’ve gone into fuel-sipping mode, just losing the edge of its manly tone.
Floor the throttle and the very changeover from V4 to V8 is so short that it gets lost in the automatic transmission’s inevitable kickdown anyway, so you really struggle to pick it up.
And, Lordy, this thing has some torque. It absolutely hurls the S8 down the road in any gear, with each shift coming with a burbling crackle as the V8 bellows its presence.
How does it compare?
There’s a little bit of the BMW X6M’s V8 in its layout – the same motor that will power the new M5 – but Audi’s V8 is smoother and more sophisticated than that. And there’s no other premium engine out there that does its neat cylinder cut-out trick. On the evidence of our first spin, it looks set to become a very serious powerplant indeed.
Anything else I need to know?
The new V8 lowers the S8’s fuel consumption to just 28.3 mpg. Next year it will find its way into the Continental GT, where it should do similar miracles for the W12 Conti’s oilwell fire fuel consumption. The S6, S6 Avant and S7 will all get a lower spec version with ‘just’ 414bhp and 406lb ft – although both should be capable of crossing the 20mpg threshold.
Then there’s the really interesting question – what happens when the mad guys at Quattro turn it into a fully-fledged ‘RS’ engine…
|Engine||3993cc V8, twin turbocharged, petrol|
|Max power||513bhp @ 6000rpm|
|Max torque||479lb ft @ 1750rpm|
|0-60||4.2 secs (claimed)|
|Top speed||155mph (electronically limited)|
|On sale||November 2011|