WHOEVER heard of improving just about every aspect of a car's performance by giving it a smaller engine?

And then designing it so that only half the cylinders work for some of the time?

To be fair, Audi is not the only manufacturer performing this kind of engineering trickery at present.

But the German brand is becoming one of the most adept at it, such is the number and variety of new, high-performance models coming to market with the famous four-ring badge on the front.

In updating both its S6 and S7 models, Audi has thrown away the naturally aspirated 5.2-litre V10 of the outgoing cars and replaced it with a 4.0-litre, twin-turbo V8.

So despite the drop in capacity, the turbos ensure the new cars out-perform their predecessors, in speed and acceleration as well as economy and efficiency.

The S6 saloon can launch itself from 0-62mph in 4.6 seconds - that's the same as Audi's own V8-engined R8 supercar.

The S6 Avant - the estate model - and the bigger S7 super coupe are just a tenth of a second slower over the same sprint.

Meanwhile, all three cars can achieve average fuel consumption of around 29mpg - although don't expect to get that if you're testing out the accuracy of those acceleration figures.

To reduce fuel consumption by as much as 25 per cent, there is a clever cylinder deactivation system that cuts in when the engine is not under load.

As you cruise along at low revs, or trickle through city traffic, four of the eight cylinders shut down until a stab of the right foot rouses them to active service again.

It's a seamless process, scarcely noticeable when driving normally.

Part of the reason for this is another innovation, an active noise-cancelling system developed from hi-fi headphones.

Because the engine is not as smooth in four-cylinder mode as in eight, engine and chassis sensors and microphones in the cabin monitor harshness and noise and broadcast a cancelling signal through the stereo system.

To the uninitiated, it's pure magic.

Audi engineers demonstrated it in a static car on a busy airport road. Even with the windows down and the engine running, the noise inside the cabin noticeably dropped when the system was switched on.

It's not clear, however, whether it will cancel out the sound of a backseat driver.

Either way, there's plenty of room for backseat drivers in all the cars, although the raked rear hatch of the S7 limits headroom.

And drivers occupying either back or front seats will be at home in elegant, classy interiors that are now an Audi trademark. Special leather and some attractive new materials, such as wood and aluminium veneers, add to the special feel.

Equipment levels are also high - they may have been around for a couple of years now but features like Google Earth images superimposed on the sat nav, head-up display and night vision still seem like something from the future.

The S7 is a big, mile-munching GT and you would happily pilot it across continents. But it's a wide car to hustle around narrow roads.

The S6 is a more manageable size, but still with plenty of room inside - especially in Avant guise.

As the figures suggest, performance is impressive and, with permanent quattro four-wheel-drive, the cars are sure-footed.

The only problem for either car is that they sit in the range above the excellent 3.0-litre diesels - and they're a good £10,000 cheaper.

True, they don't have the out-and-out performance of the S-cars but they're still very quick and composed transport.

UK order books are expected to open in May and first deliveries are anticipated in July. 

Prices are from £53,995 for the S6, the S6 Avant will cost from £56,050 and S7 from £61,995.