Caught on camera during early development testing in Avant form, the performance model will trade its predecessor's TFSI eight-cylinder unit for the 2.9-litre motor, offering more performance and better fuel efficiency.
While it's plausible that the hybrid V6 powertrain of the Panamera E-Hybrid could also be used for the next S6, the lack of plug-in ports on the spotted test car (which appears to have a conventional fuel filler cap) suggests that the simpler set-up of a turbocharged six-cylinder will be used.
When it goes on sale, the S6’s six-pot heart will make it the most potent A6 variant offered. It'll beat the 335bhp 3.0-litre V6-engined 55 TFSI model, driven recently by Autocar, although it will eventually be overtaken by an RS6 model that is likely to use brand's latest 4.0-litre V8 engine.
As with its forebears, the next S6 will be sold exclusively with quattro all-wheel drive, which should provide the car with off-the-line traction to enable a 0-62mph time of little more than four seconds — this would be a six-tenth improvement on the outgoing model and rank it around a second ahead of the 55 TFSI. Evidence for this potential comes with the smaller and lighter RS5, which can reach 62mph in 3.9sec.
The latest A6 range uses a new hybrid aluminium chassis with five-link suspension, featuring bolstered front and rear subframes. The benefits of this set-up are a reduction in structural weight — this could ensure the car’s kerb weight also shrinks — and an increase in structural rigidity. The range also comes available with a complex all-wheel steering system, which could be offered as standard with the S6 to improve low-speed agility and high-speed stability.