What is it?
Up until now, BMW’s twin-turbo straight six – as fitted to the 535D amongst others – has defined the high performance six-pot diesel. But now Audi has an answer, matching exactly the BMW’s 309bhp and gently exceeding it for torque by offering 479lb ft of twisting force compared to the BMW’s 465lb ft.
This new Biturbo engine is the third and most potent of a trio of 3-litre V6 diesels offered in the new A6 range, all of which use different styles of transmission. With CVT and twin-clutch S Tronic ‘boxes used for the low and mid-power V6s respectively, the Biturbo reverts to an 8-speed Tiptronic in order to handle the rampant torque on offer.
Using a sequential configuration, the small turbine takes care of low-rev response and a much larger turbocharger provides higher rev power. A vacuum valve passes the baton between the two, beginning to open by 2,500rpm and at 4,500rpm handing the workload solely to the larger turbo.
What’s it like?
The results, sampled first in the new A6 Avant, are deeply impressive. Utilising the traction advantage of four-wheel drive, the new engine blasts this big, relatively heavy car from rest to 60mph in just over five seconds, and will easily run into the 155mph limiter.
But what really appeals is the manner in which the new engine achieves these numbers: it revs convincingly past 5,000rpm, and in ‘Sport’ mode the trick exhaust manages to make it sound appealingly aggressive.
This isn’t wasted in the new A6, because as we’ve said recently, while it’s not the most entertaining of drives it does feel a lot less inert than previous iterations, helped by the reduced front overhang and the Quattro differential fitted here.
Should I buy one?
Predictably, real-world pace is prodigious, but we’ve suspicions that the sports suspension and big wheels of this model may mean an over-firm ride in the UK. However, when you combine the performance above, with around 44mpg and only 169g/km of C02, plus the usual high quality cabin and estate practicality, it does make for a desirable package.
Audi A6 Avant 3.0 TDI Biturbo S-Line
Price: £46,000; Top speed: 155mph (limited); 0-62mph: 5.3sec; Economy: 44mpg; Co2: 169g/km; Kerb weight: n/a; Engine type, cc: 2967cc V6 twin-turbo diesel; Power: 309bhp at 3900-4500rpm; Torque: 479lb ft at 1450-2800rpm; Gearbox: 8-spd Tiptronic