Audi has released the first images and technical details of the new S6 and S7 Sportback models, with no teasers or build-up.

The range-topping versions of the latest A6 and A7 have switched from V8 petrol power to use a V6 diesel unit mated to an electric compressor and 48V mild-hybrid system.

Producing 345bhp in all forms, the new engine is nearly 100bhp less powerful than the eight-cylinder unit in the old S6 and S7. It counters with significantly more torque, putting out a peak of 516lb ft at 2500rpm.

The electric compressor, also used in the V8 diesel Audi SQ7, is utilised to fill any torque gaps at low revs before the turbo can spool up. Responding in 250 milliseconds, it works up to an engine speed of 1650rpm and spins up to 70,000rpm.

The result is a 0-62mph time of 5.0sec in the S6 saloon, increasing by a tenth of a second in the S6 Avant and S7 Sportback. The top speed is, as usual, limited to 155mph.

Using the now-familiar 48V mild-hybrid system found on lesser A6s and A7s, which allows energy recovery under acceleration and stop-start operation below 14mph, the S6 and S7 promise between 43 and 46mpg depending on bodystyle, wheel and tyre choice. CO2 emissions go as low as 164g/km depending on spec.

The S6 and S7’s chassis receives specific sports suspension with adaptive damping and a 20mm lower ride height (10mm lower on S7), with the option of more comfort-focused adaptive air suspension instead. All-wheel steering is also an option, while quattro all-wheel drive is standard.

In keeping with the more subtle nature of S models compared with RS variants, styling tweaks are subtle and include quad tailpipes at the rear, tweaks to the bumpers front and rear and 20in wheels. S badging and a redesigned grille also feature, while the interior includes sports seats and new trim material options.