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The Audi A6 is now the fastest diesel model in Australia, courtesy of a new twin-turbo V6.
Audi has been trying to make diesel power sexy since it entered the world famous Le Mans 24-hour endurance race in 2006 with the R10 that was powered by a 5.5-litre V12 oil-burner. It won that year and has rarely lost since, with a variety of diesel racers.
The new Audi A6 3.0 TDI Biturbo doesn’t gain either of Audi’s sportier S or RS badges, but it does the two key things those Le Mans race cars did: be both quick and economical.
For the fast bit, the A6 3.0 TDI Biturbo will accelerate from 0-100km/h in 5.1 seconds. For the frugal part, the sedan’s official consumption is rated at just 6.4 litres per 100km.
The same engine is also available in the A7 Sportback, with the same efficiency but slightly less performance (0-100 in 5.3 seconds) for the coupe-style four-door that’s based on the A6.
With diesel power accounting for 58 per cent of A6 sales locally it’s easy to understand Audi Australia’s enthusiasm for importing the regular range’s new flagship (not counting the S6 and upcoming RS6).
The Audi A6 3.0 TDI that features a single turbo diesel engine with 180kW of power and 580Nm of torque comprises more than a quarter of the sedan’s sales.
But if buyers don’t mind using an extra half litre of diesel every 100km, the ‘biturbo’ version overshadows it for outputs (up 50kW and 70Nm) and speed (a full second quicker in the sprint to 100km/h).
Audi’s new twin-turbo diesel is related to the other 3.0-litre TDI but is 4kg lighter (to 209kg) and features a number of significant upgrades that include revised cylinder head, lowered compression ratio, improved piston cooling and of course those two sequential turbos that help produce 230kW and 650Nm.
It’s a little’n’large show, with a smaller turbo with variable vanes controlling the amount of air coming through and providing assistance at lower revs.
From about 2500rpm, a changeover valve connecting the two turbos starts to open to bring the larger turbo into play. About a thousand or so revs higher, and that valve is completely open as the small turbo becomes redundant and its larger brother provides the engine boost at higher revs.
How does it work in the real world? Well, almost brilliantly.
We say almost only because there is a moment of hesitation from the Audi A6 biturbo diesel when you ask for a fair degree of acceleration from lower revs.
It’s not a long delay but it is noticeable, though once the small turbo warms to its task, and especially once the bigger turbo is on song, the A6 3.0 TDI biturbo surges along, devouring country kilometres with contemptible ease.
It has the kind of mid-range acceleration that warrants regular checks of the speedo because you’ll often find yourself travelling faster than what your effortless progress suggests.
And at the freeway-legal limit of 110km/h, just 1400rpm is registered on the rev counter. One surprise, though, is that the A6 Biturbo struggles to maintain a set cruise control speed on undulating sections of freeway.
It’s not ideal in a country notorious for its over-zealous highway patrols.
The V6 is aided by a ZF eight-speed auto that is exclusive to the Biturbo diesel in the Audi A6 range, better able to cope with the extra torque than the seven-speed dual-clutch autos found in the other V6 petrol and diesel variants.
The auto is as suave and precise as it is in a range of models from other (mainly luxury) brands, including a large number from BMW.
Leave the auto in Drive and it will also allow revs to climb all the way to the 5200rpm redline before changing up.
Most diesel engines won’t rev that high yet in the Audi A6 biturbo, revving to the 5000 marker on the tachometer isn’t detrimental to maintaining momentum even though the engine’s maximum power arrives 500rpm earlier.
It doesn’t sound bad getting there, either. Diesels aren’t renowned for their sporty soundtracks – including Audi’s 300km/h-plus Le Mans race cars – but Audi has set out to provide some aural companionship for that mighty pace.
Each of the Audi A6 biturbo’s tailpipes incorporates an electronic loudspeaker that plays with the harmonics of the exhaust sound that are then transmitted to the cabin via the windscreen and bodywork vibrations.
You need to choose Dynamic mode from Audi’s Drive Select system to engage the ‘sound actuator’, and there’s a noticeable change in pitch and a deepening growl when you’ve done so.
It sounds good, even if the still relatively restrained note is unlikely to convert petrol V8 lovers any time soon.
The rest of the Biturbo experience is familiar from other Audi A6 models.
That does mean steering and handling that could be more involving and entertaining in comparison to the BMW 5 Series, Mercedes-Benz E-Class and Jaguar XF, but also body control and ride comfort that are still well judged.
And then there’s that interior that not only provide plenty of space for occupants but is also the segment benchmark for quality and design by quite some margin.
The Audi A6 3.0 TDI Biturbo is priced from $118,800, which is a $11,300 premium over the single-turbo 3.0 TDI variant and a touch more than the Jaguar XFS 3.0D (from $115,500).
Crucially, though, it undercuts the rival BMW 535d (from $121,500) and Mercedes-Benz E350 CDI (from $136,485).
The current Audi A6 is already the most convincing of all its generations. The 3.0 TDI Biturbo version is a tempting variant for those who would like to match sports car acceleration with small car fuel economy.