The W principle
The new Audi twelve-cylinder engine is unparalleled by past technology - despite the fact that there have already been examples of this W-engine design in automotive history. The legendary 1920s Rumpler "tear-drop" car, for example, for which its designer developed a six-cylinder engine in 3x2 formation. Or, just a few years later, the world record car driven by Campell, Seagrave and Cobb: this was powered by a W12 aircraft engine with a capacity of 24 litres and 502 bhp.
And Audi too has already made use of a W12 engine in the past: this one produced 509 bhp in the legendary Avus super sports car study, presented in 1991.
A direct comparison with these engines clearly reveals the special feature of the Audi engine. Unlike its historical predecessors, it is not a W-engine in the classic sense with three separate cylinder banks, where three connecting rods are mounted on a single crankpin. The new twelve-cylinder engine, which the Audi design engineers have developed together with their Volkswagen colleagues, is different: in this case, there are two connecting rods per crank pin.
A glance at the engine's cylinder blocks shows that two ultra-compact inline V6 units are combined to produce a single engine. Each of the two cylinder banks contains six cylinders at an angle of 15 degrees. This offset arrangement makes an ideal synthesis of the very compact width - compared with the classic V6 - and the very short length of a four-cylinder engine.
Joining these two units at an angle of 72 degrees to produce a twelve-cylinder engine has a third advantage: the height of the engine is considerably less than that of a "genuine" W12, which means that the aerodynamically beneficial, flat silhouette of the A8's front end can remain unchanged.
And, a further advantage, the unmistakable sporty aura of the Audi A8 design has thus also been retained in the top-of-the-range version, where perhaps it is most expected.
Another advantage of this design is the high rigidity of the engine as a whole. In conjunction with the transmission, this means extremely low levels of vibration. This translates into a standard of vibrational comfort which surpasses even the high level expected of a conventional twelve-cylinder engine.
The heart of the W12 engine is the crankshaft running in seven bearings and weighing just 20.5 kilograms. The crankpins are offset to achieve a constant firing sequence as on a V6 engine.
With dry sump lubrication
As a gesture of respect to its particularly high performance, Audi's W12 engine has dry sump lubrication. In contrast to conventional wet sump lubrication, the oil pumps supplies the engine with oil from a separate oil tank mounted to the vehicle. This oil tank is situated behind the right-hand headlight and is connected to the engine by two hoses.
A dual-line suction pump flanged onto the pressurised-oil pump ensures that the engine oil is returned reliably to the oil tank. The flat oil sump has two specifically positioned drain points, to ensure a supply of engine oil in all operating statuses. The oil pump is driven by a chain directly from the crankshaft.
A water-type oil cooler on the left side of the engine near the oil sump ensures efficient temperature control.
This is a system rarely found on production vehicles, in just a few high-performance sports cars. The greatest advantage of dry sump lubrication is that it allows an optimum supply of oil to the engine even at high levels of longitudinal and lateral acceleration.