Newly developed V10 with FSI technology and beefy torque characteristic
For the first time in its history, the Audi brand is presenting a ten-cylinder engine – the new V10. The Italian super sports car brand Lamborghini, a subsidiary of Audi, likewise uses the ten-cylinder engine as a supreme source of power in its Gallardo model. The V10 in the new Audi S6 is a new development. It first appeared in the Audi S8 and now has been specifically returned to propel the top model of the Audi luxury range.
In a departure from the principle used by Lamborghini, the V10 features petrol direct injection FSI on the Audi models. This combination of ten cylinders and FSI technology gives Audi a unique technological position on the market.
A ten-cylinder engine is the ideal design for realising sporting aspirations. It has the edge on a comparable twelve-cylinder unit thanks to the smaller number of components, resulting in lower moving masses and less internal friction; the fuel is consequently put to very efficient use. A V10 is moreover considerably lighter and more compact than a conventional 12-cylinder engine – including all its add-on components, the engine of the new Audi S6 is just 685 millimetres long, 801 mm wide and 713 mm high. The bare engine measures 560 mm in length.
Although an eight-cylinder engine would be even more compact, to make it into the five-litre-plus class it would need large, heavy pistons and connecting rods, so its ability to rev freely would be impaired as a result. It is no coincidence that many competitors have generally concentrated simply on high torque with their large-capacity V8 engines, rather than attempting to squeeze sporty performance out of them too.
The 435 bhp V10 in the new Audi S6 belongs to the next generation of Audi V-engines, all of which have a 90-degree included angle and a spacing of 90 millimetres between cylinder centres. Its two banks of cylinders are offset by 18.5 mm.
Key areas of the Audi version have been reengineered compared with the engine in the Lamborghini Gallardo. The bore, for instance, has been increased from 82.5 to 84.5 millimetres. Its stroke is 92.8 mm, and its displacement 5,204 cm3.
The crankcase of the Audi ten-cylinder engine is produced by low-pressure die-casting, from a hypereutectic aluminium alloy. This technology renders separate cylinder liners superfluous; the cylinder barrels are instead honed directly from the material by mechanically exposing the hard silicon crystals. A so-called bedplate design – an intermediate frame – gives the crankcase extremely high torsional rigidity and improves its vibrational behaviour. Its cast-in bearing bridges, made from grey cast iron, reduce thermal expansion and keep the amount of play at the main crankshaft bearings within tight tolerances.
The high-strength connecting rods are made from forged steel, and the pistons from an aluminium alloy. At the rated engine speed, each of them covers an average distance of 21 metres per second. With its crankpin offset of 18 degrees, the V10 fires at the ideal spacing of 72 degrees crankshaft angle. A balancing shaft located between the cylinder banks eliminates the free inertial forces of the first degree and also contributes towards the engine's notable refinement.
All four camshafts of the ten-cylinder engine (two per cylinder bank – the DOHC principle) can be adjusted continuously by 42 degrees crankshaft angle via hydraulic camshaft adjusters, depending on the load and engine speed. In this way, filling of the combustion chambers is optimised across the entire engine speed range and the engine response is enhanced.
The camshafts – complete with the balancing shaft, the oil and water pump and the auxiliaries – are driven by maintenance-free chains running on the reverse side of the engine.
The valves – 40 in total – are actuated via roller cam followers with hydraulic valve-play compensation.
The diameter of the valves on the intake side is 32.5 millimetres, and 28.0 mm on the exhaust valves. The highly-loaded exhaust valves are sodium-filled, which ensures a better cooling effect.
The V10 in the new Audi S6 uses the FSI petrol direct injection principle; this permits a high compression ratio of 12.5:1 and a correspondingly effective combustion process.
FSI technology has impressively demonstrated its dynamic potential in motor sport – the R8 racing car equipped with it participated in the Le Mans 24 Hours five times for Audi, emerging as the winner on four of those occasions.
In the Audi S6, the FSI technology is managed by a highly advanced Bosch Motronic bearing the designation MED 9.1, operating with two separate control units according to the master/slave principle.
Unlike conventional indirect manifold injection, the FSI common rail injection system injects the fuel directly into the combustion chambers in precisely metered amounts, at a pressure of up to 100 bar. This results in an extremely homogeneous fuel/air mixture, benefiting the efficiency of the combustion process. An internal cooling effect moreover takes place, allowing the engine's basic compression ratio to be raised to a high 12.5:1. A highly efficient combustion process is the result.
The magnesium two-stage variable intake manifold is respirated via two separate air paths with two air filters. The variable intake manifold incorporates electronically controlled tumble flaps that induce a tumbling motion in the air drawn in at low engine speeds and loads; this enhances the efficiency of the combustion process inside the engine even further.
The two-stage layout of the magnesium intake manifold serves the same purpose. Depending on the load and engine speed, the longer manifold length (675 mm) is activated to provide ample torque at low and medium engine speeds, and the shorter manifold length (307 mm) to ensure high power output at higher engine speeds.
The design of the single-pipe manifolds likewise contributes to the dynamically optimised charge cycle; it is matched precisely to the firing order of the V10. On each cylinder bank, the exhaust ducting of the first and second cylinder and of the fourth and fifth cylinder is combined; it only converges with the exhaust ducting of the third cylinder relatively far down. Four main catalytic converters take charge of exhaust emission control.
The powerful ten-cylinder engine has been optimised for high torque as well as high engine power. It achieves 435 bhp (320 bhp) at 6,800 rpm, and musters up 540 Nm of torque at engine speeds as low as 3,000 to 4,000 rpm.
Over 90 percent of the torque is available from as low as 2,300 rpm. The V10 exhibits highly spontaneous throttle response and very refined running, and under load it also produces a sonorous, sportily gutsy acoustic backdrop, as befits a dynamic vehicle of Grand Touring calibre. The V10 is a far cry from a rough-diamond sports engine: for all its sporty character, this ten-cylinder engine is very low-vibration and exhibits plenty of refinement.
For Audi, lightweight design is a philosophy that has implications for every area of a vehicle. As in motor sport, the engineers developing the S6 fought to save every gram of weight possible. Thanks to its compact design and thinner walls, the V10 weighs just 220 kilograms. A dynamically balanced distribution of axle loads and impressive road behaviour are the result. For the same reason, the battery and the power management are housed in the luggage compartment.
The V10 lends the Audi S6 the road performance of a Grand Touring: the Audi S6 sprints from 0 to 100 km/h in 5.2 seconds, and the Avant estate-car version takes just one-tenth of a second longer.
The car effortlessly reaches its top speed of 250 km/h, the point at which the electronic governor smoothly cuts in, this performance being enhanced among other things by its low drag coefficient of cD 0.31.
The engine consumes a modest 13.4 litres of Super Plus fuel per 100 kilometres.
The S6 weighs 1,910 kilograms (S6 Avant: 1,970 kg), including the dynamic, sure-footed quattro permanent four-wheel drive. Every horsepower consequently has to propel just 4.39 kilograms (S6 Avant: 4.53 kg) – the power-to-weight ratio of a top-notch sports car.
The equipment, data and prices stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.