A NEW breed of performance models is on the way from Audi with each designed to get the best from turbo power.

Out goes the normally aspirated 5.2-litre V10 monster fitted to the previous S6 and S8 super saloons and in comes a turbo charged four-litre V8 which features some very clever fuel saving technology.

The result is a new range of S machines which now includes for the first time an S7 Sportback four-door coupe.

Audi reserves the S badge for the higher powered versions of its regular models and with quattro all wheel drive they have gained a reputation as luxury cars with genuinely sporty credentials.

They may sit in a niche below Audi's ultra quick RS line up but they pack a mean punch.

In the new S8 - the flagship of the range - 0 to 60 flashes up in 4.2 seconds and with its twin turbos on song there is 520bhp on tap.

That's an incredible 130bhp per litre from the V8, eclipsing the performance of the previous V10 engine by almost a second.

The punch of the S8 is enhanced by an eight speed auto box and a lightweight aluminium body structure which makes this a limousine-sized car that tips the scales at less than two tonnes.

But Audi's trick with the new engine comes with what it calls cylinder on demand technology which switches off four of the eight pots under light throttle loads, significantly improving economy.

Audi claims the S8 is capable of averaging 28mpg with emissions of 235g/km making it some 25 per cent more fuel efficient than the previous model.

From the driving seat, the change from four to eight cylinder running is unnoticeable save for a message on the instrument panel that the car is operating in four cylinder mode and while we failed to match Audi's official figure we did manage 24.5 to the gallon and that's still impressive in a car of such size.

Adaptive air suspension and a sport differential controlling the quattro all wheel drive make for plenty of grip and the ride is super smooth and surprisingly agile.

The S8 is also fitted with a new dynamic steering system which adjusts ratios according to speed. It's designed to give greater control close to the car's limits but it can feel a little impersonal in a vehicle which in every other aspect is a first class driver's machine.

With grey faced instruments, plenty of leather and a T-shaped bite-sized gear selector the interior is undeniably classy, its ambience aided by a noise cancellation device which generates ‘white sound' to mask wind and road rumble.

When cruising the cabin is as quiet as a limo should be but under acceleration there's still enough V8 roar from the twin exhaust clusters to create a smile.

At a basic price of £77,900 the S8 is in a league of its own and extras - ceramic brakes for example add £8,650 - can send the price soaring to more than £100,000.

The S6 and S7 come in at £53,995 and £61,995 respectively with S6 Avant estates priced from £56,050.

While not quite as well endowed as the S8 they are certainly impressive and all come as quatrros with the noise reduction system and cylinder on demand technology as standard.

The engines do not use the same amount of boost but still develop 420bhp giving the S6 a 0 to 60 time of 4.6 seconds with slightly heavier Avant and S7 clocked at 4.7.

As with the S8 the top speed is restricted at 155mph yet fuel economy is even greater with all three models averaging more than 29 to the gallon. Emissions for the S6 and S7 are 225g/km and 226g/km in the Avant.