What's it like?
We had a brief opportunity to test the A6 TDI concept back-to-back against a conventional 550bhp RS6, which uses a twin-turbocharged V8.
From a standing start the instantaneous wall of torque developed by the 3.0 TDI put the nose of the A6 concept ahead for a couple of hundred metres before the more powerful car pulled away.
The existing eight-speed torque converter automatic is due to be replaced by a new seven-speed dual-clutch transmission and this should make a further improvement to response.
Currently the single-turbo TDI produces a peak of 322bhp, and 479lb ft torque between 1500rpm and 3500rpm. The electric compressor’s job is to boost torque below 1500rpm, creating the slingshot response and proper RS get-up-and-go initial acceleration. When the turbo comes on song, the electric compressor is effectively removed from the intake system via a bypass valve.
Exploiting that torque window and resisting the temptation to let revs climb too high is the best way to make rapid progress.
On the twisting test track, this truck-like pulling power proved ideal, the A6 concept lunging eagerly out of slow corners and proving satisfyingly flexible in between. Figures back up the subjective impressions, with acceleration from 37mph to 75mph in sixth gear improved from 13.7 seconds for the standard car to 8.3 seconds with the electric boosting.
The concept sounds good too, the usual extreme levels of refinement dialled back a touch allowing engine and exhaust to produce a satisfying growl. If the A6 concept lacks anything in terms of sheer fun, it’s the ability to rev like a petrol engine with the spine-tingling rush that brings.
Should I buy one?
There are no official production plans for the A6 concept yet, but Audi is clear about the fact it will offer customers high performance diesels at some stage.
The first electric compressor is due to enter production in a new SQ7 in 2016, complete with a new 48-volt electrical architecture running in parallel with the existing 12-volt system.
Given the cost and complexity of developing the new system, it is unlikely Audi will stop there.
Audi A6 TDI concept
Price £79,500 (est); 0-62mph TBC; Top speed TBC; Economy TBC; CO2 TBC; Kerb weight 1720kg (standard A6 quattro); Engine type, cc V6 2967cc V6 turbodiesel with electric boost, 2967cc; Power 322bhp; Torque 479lb ft at 1500 to 3500rpm; Gearbox 8-speed Tiptronic