The next Audi S8 and S6 super-saloons are to replace the 5.2-litre V10 engine for a new twin-turbo 4.0-litre V8.

Audi has confirmed that to meet emissions targets and follow consumer demand, the new engine has been developed to provide more power and performance along with up to 25% better fuel economy.

Two derivatives of the same engine will be used in the S6 saloon and Avant, the S7 Sportback and the S8. The first three will share a 414bhp, 406lb.ft version and all hit 62mph in less than five seconds, while the flagship S8's wick will be turned up to 513bhp and 479lb.ft for 0-62mph pace of 4.2 seconds.

However, all four models have achieved almost 30mpg in the standard European fuel economy tests, with CO2 output between 225g/km and 235g/km.

Large fuel economy improvements have been made possible with the introduction of a cylinder deactivation system that shuts four of the V8's cylinders off under light engine loads, turning it temporarily into a V4. Under these light engine loads, where refinement is most important, the new V8 Audis will use active noise cancelling.

To make sure the cars cruise with all the smoothness and refinement that Audi's premium saloon customers expect, active noise cancelling will reduce the impact of any undesirable noise within the cabin. Microphones measure the offending sounds and the stereo speakers transmit exactly opposing frequencies, minimising the apparent noise intrusion.

Although all four new models will have permanent quattro four-wheel-drive, the S6 duo and S7 Sportback will have clever rear differentials that allow power to be shuffled to the rear wheel that can best make use of it. The S8 also has an automatically locking centre diff to allow it to find even more traction under hard acceleration.

The S8, which will cost from £77,900 on the road, will also be fitted with adaptive air suspension that can alter the ride height according between three levels to give what Audi calls a `multi-faceted driving experience'.

The S6 saloon and Avant will cost £53,995 and £56,050 respectively, while the S7 Sportback will be more expensive, at £61,995.