12 per cent economy improvement
As a result, the A8 L W12 can cruise serenely to 62mph in just 4.9 seconds, and continue to a seemingly effortless governed top speed of 155mph. And with the help of FSI technology, fuel economy belies these figures, with up to 23.5mpg achievable according to the combined cycle test – a 12 per cent improvement over the outgoing model which results in CO2 output of 278g/km.
Thanks to its cylinder arrangement, which forms the ‘W’ shape that gives this model its name, the W12 engine is exceptionally compact at just over 50cm in length and 70cm in both width and height, and its overall weight of 247kg is also impressively low helped by high aluminium content.
The two camshafts within each of the engine’s aluminium cylinder heads operate 48 valves by way of low-friction roller cam followers, and are themselves driven by chains from an intermediate shaft. The cylinder heads themselves have been extensively modified to enable FSI technology to be incorporated, and as a result fuel is injected into the combustion chambers at a pressure of up to 130 bar, giving a high 11.8:1 compression ratio that boosts power output and efficiency.
New efficiency measures
The crankshaft and timing chains have also been reworked to reduce friction, and a recuperation system recovers energy that would otherwise be lost when the car is braked. An innovative thermal management system also shuts down the coolant circuit for a time after the cold engine has been started. This warms up the engine oil more rapidly and shortens the operating period in which friction is still high.
Efficiency is also boosted further still by the new eight-speed tiptronic automatic transmission, which shifts smoothly and quickly, with the individual gears closely spaced but with a generous overall spread from low to high. Gear shifts are performed electronically (“shift by wire”) via the yacht-style selector lever or steering wheel paddles.
The centre differential, the main component in the quattro permanent all-wheel drive train, allots up to 60 per cent of the torque flow to the rear axle and 40 per cent to the front in regular driving conditions. If driving conditions warrant it, up to 60 per cent of the torque can be sent to the front, or 80 per cent to the rear. An optional sport differential can split this torque input actively between the left and right rear wheels. Its responses can be fine-tuned, along with throttle response, steering assistance and transmission shift points, at the touch of a button via the built-in Audi drive select adaptive dynamics system.
Thanks to its advanced adaptive air springs, aluminium-intensive suspension and latest generation quattro all-wheel-drive, the long-wheelbase Audi A8 manages to combine the polished ride refinement expected of a luxury car with handling poise and agility that would normally characterise performance saloons from one or two classes below.