New V10 with FSI technology adopted from the world of motor racing
In outfitting the S8 with the V10, Audi is introducing an engine technology that has long been demonstrating its performance potential in the world of Formula 1 racing. The Italian super sports car brand Lamborghini, a subsidiary of Audi, likewise regards the ten-cylinder engine as synonymous with dynamic power. This engine concept has a much more sporty emphasis than a comparable twelve-cylinder power unit. Ten-cylinder engines are more compact and lighter; thanks to the smaller number of components, they have lower moving masses and less internal friction.
The 450 bhp V10 is the second generation of Audi V-engines, all with a 90-degree included angle and a spacing of 90 millimetres between cylinder centres. Key areas of the Audi version have been reengineered compared with the engine in the Lamborghini Gallardo. The bore has been increased from 82.5 to 84.5 mm; the stroke is 92.8 mm and the displacement 5204 cm3. A so-called bedplate structure – an intermediate frame – reinforces the extremely compact crankcase, which is made from cast aluminium.
With its crankpin offset of 18 degrees, the V10 fires at the ideal spacing of 72 degrees crankshaft angle. A balancing shaft located within the "vee" eliminates the so-called free inertial forces of the first degree and also contributes towards the engine's notable refinement. All four camshafts can be adjusted continuously by 42 degrees crankshaft angle, depending on load and engine speed, to optimise filling of the combustion chambers and thus enhance the power output. They are driven by no-maintenance chains and actuate the 40 valves via roller cam followers.
The V10 in the new Audi S8 uses FSI petrol direct injection. This permits a high compression ratio of 12.5:1 and a correspondingly more effective combustion process based on a lambda value of 1. The common rail injection system delivers the fuel directly to the combustion chambers in precisely metered amounts, at a pressure of up to 100 bar.
The two-stage magnesium variable intake manifold incorporates electronically controlled tumble flaps that induce a swirling movement in the air drawn in. Four close-coupled main catalytic converters take charge of exhaust emission control for the V10 of the Audi S8. FSI technology has impressively demonstrated its potential in motor sport – the R8 racing car equipped with it participated in the Le Mans 24 Hours on five occasions for Audi, winning the race on four of those occasions.
The powerful ten-cylinder engine is designed for impressive torque as well as engine power. It generates 450 bhp at 7,000 rpm, but musters up 540 Nm of torque at just 3,500 rpm. 90 percent of the torque is available from as low as 2,300 rpm. The V10 exhibits spontaneous throttle response and very refined running, and under load it also produces sonorous acoustics, as befits a dynamic car.
The V10 imparts the luxury saloon with the road performance of a high-calibre sports car. The Audi S8 races from 0 to 100 km/h in 5.1 seconds. The speed is not governed electronically until the needle reaches 250 km/h. The engine shows a distinctly modest thirst, needing only 13.9 litres of fuel per 100 kilometres – a figure achieved partly thanks to the consistent use of lightweight design, which clearly sets the A8 range apart from its competitors. With its innovative aluminium body, the Audi Space Frame ASF, the S8 weighs just 1940 kilograms, including the dynamic, sure-footed quattro drive. On the new Audi S8, every horsepower has to propel just 4.31 kilograms – the power-to-weight ratio of a sports car.