Engineered in a joint program between Audi and Bentley, which also plans to fit it to the Continental GT and GTC early next year, the 90-degree unit is the first recipient of a new cylinder on demand system that automatically shuts down four-cylinders on light throttle loads for added fuel saving.
As fitted to the S8, it delivers 69bhp and 80lb ft more than the old model’s naturally aspirated 5.2-litre V10.
What's it like?
The gains, however, are not only evident on paper. Right from the off, the advanced unit feels more muscular and altogether more responsive.
On light throttle loads in third gear or higher there are no telltale signs apart from a digital read-out within the instrument binnacle that the new engine’s advanced electronic management system has chosen to close down the inlet and exhaust valves of cylinders 2, 3, 5 and 8 in the interests of fuel saving and lower emissions.
The operation of the cylinder deactivation system on the pre-production prototype we drove was absolutely seamless, both from a mechanical and acoustic standpoint. This perception is achieved, in part, by what Audi calls active noise cancellation – a system used to suppress the typical hum and what the German car maker describes as other intrusive acoustic elements of the engine when running in four-cylinder mode.
With added throttle, the delivery is uncannily smooth and extremely linear across a wide range of revs. There’s no discernible turbocharger lag of any kind, just a compelling and boundless seam of energy all the way from the 800rpm idle all the way to the 6500rpm cut-out point. And to top it all off, there’s a lovely deep burble through the exhaust that grows in intensity as you pile the revs on.
In lower gears, a combination of the new engine’s heady torque loading and the latest iteration of Audi’s Torsen four-wheel-drive system provides for rabid straight-line speed, as evidenced by Audi’s official 0-62mph time of just 4.2sec – or 0.9sec faster than the old S8. Considering its relatively small capacity by performance car standards, its in-gear performance is extraordinary.
Where the big Audi really excels is on damp roads. Big applications of throttle out of slow corners fail to upset its composure, even in the wet. As an all-season proposition, it is going to take some beating.
Audi has also tweaked its eight-speed automatic gearbox with alterations to the torque converter and a new electronics package. It shifts with great conviction, both on light loads and wide open throttle, while offering stop/start and brake energy recuperation functions that helps the new S8 achieve a 6.3mpg improvement in combined cycle consumption at 27.7mpg.
Should I buy one?
Definitive judgment will come when we get to put a production version the new S8 through its paces on more familiar blacktop later this year. For the time being, however, the pre-production prototype driven here suggests the S8 may have finally come of age. More miles are needed to discover whether our concerns about the synthetic feel of its steering are justified. But we’ll be very surprised if our impressions of improved ride quality aren’t felt on British roads. The new model feels much more settled, even on the optional 21-inch wheels and giant 265/35 R21 Pirelli P-Zero tyres fitted.
Price: tba; Top speed: 155mph; 0-62mph: 4.2sec; Economy: 27.7mpg; CO2: 237g/km; Kerb weight: 1975kg; Engine type, cc: V8, 3993cc, twin turbo, petrol; Power 513bhp at 5800rpm; Torque: 479lb ft at 1700rpm; Gearbox: 8-spd automatic