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.