The heart of the S6 is a north-south nose-mounted 3.0-litre V6 equipped with a 48V electrically driven compressor whose output keeps the turbocharger spinning, even when the crankshaft speed is low, to cut spool-up time and reduce accelerator lag. The system also incorporates a 48V belt-driven integrated starter-generator that under acceleration contributes to peak outputs of 344bhp at 3850rpm and 516lb ft of torque at 2500-3100rpm. When the car is coasting or on the overrun, it collects power in a 0.48kWh battery for later use in acceleration.
The hybrid power is directed through an eight-speed dual-clutch automatic gearbox to a permanent four-wheel-drive system, which at extra cost can be specified with a sport central differential to sharpen the car’s agility in corners.
Audi says the mild-hybrid part of the powertrain contributes around 2-3mpg to real-world fuel consumption and helps the whole system run cleaner. The official WLTP combined fuel consumption figure is 36.2mpg and the CO2 output is 164g/km – both impressive results for a five-metre, two-tonne saloon that can pull a 5.0sec 0-62mph time and reach a governed 155mph in very short order.
You can easily distinguish the S6 from its cooking A6 relatives by its different, sportier front apron with wide air inlets either side, its aluminium-look mirror caps, its distinctive wheel designs and its special rear diffuser. Plus badges, of course. Inside, it gets various fascia and door-mounted inlays in aluminium, special sports seats and a very high-equipment specification. Every S6 also comes with sports-oriented suspension with variable damper control. You can specify adaptive air suspension, while other key options include ceramic brakes and dynamic four-wheel steering.
None of the above prepares you for the surprise of starting the engine. The second it bursts into life, you’d swear you were sitting behind a well-schooled, big-capacity petrol V8, so evocative is the sound it makes. Audi’s engine developers have judiciously equipped the system with discreet sound generators, and they really work. Start driving and the impression increases. There’s lots of torque at low revs and the throttle response, although not quite instant, is as good as many an old-school V8 and as strong. The S6 accelerates powerfully through the speed range, pulling 5000rpm on change-up if you can find the place to hold it flat, otherwise slipping quickly, quietly and effortlessly through successive gears (its precise behaviour varied by your choice of driving mode: Sport, Normal or Economy).
The handling is very good but falls short of inspirational. The S6 is heavy for its class and has a good deal of nose weight, so the turn-in is decent without being as adjustable or energised as some. The same goes for holding a line in long, fast bends. But it’s accurate and stable, and as far as we were able to tell in dry, early summer conditions, its traction is terrific. Audi still steals a march on competitors by offering four-wheel drive, although the driver has to contend with extra weight and its consequences.