“Audi’s S4 quattro
  holds all four aces —
  four doors, four-wheel
  drive, four point two
  litres and (two) banks
  of four cylinders…”

THERE'S AN OBVIOUS CLUE
to the character of the S4 quattro. And it's as obvious as the new single-frame Audi grille. While everyone thinks they know what the 'S' stands for, they could be wrong. Try 'Surprise'. Externally, the S4's compact executive body subtly underplays its performance potential. But lift the bonnet and you will be surprised by what Audi's engineers have shoehorned into an A4 engine bay — a compact 4.2-litre eight-cylinder powerhouse that delivers a peak output of 339bhp along with 302lb ft of torque. Easy figures are zero to 62mph acceleration in 5.6 seconds, 0-124mph in 20.6 seconds and an electronically-limited top speed of 155mph.

But under the bonnet is not the only place you will find a surprise —
it's also cleverly built into the car's understated presence. Not that
this should really come as a surprise though, because Audi has a long tradition of visually playing down the performance potential of its high-performance models. At a casual glance the S4 looks much like any other A4, albeit riding on a chic set of exclusive 8J x 18-inch 6 x flat-spoke alloys shod with 235/40 Continental SportContact tyres.

So, look closer for the subtle hints to what the S4 is all about. The most blatant of these is the small 'S4' badge on the grille — one you'd have to be looking for to spot. Colour-coded bumpers with large air inlets in the nose, a contrasting titanium-coloured inner housing for the xenon headlights, four chromed large diameter oval-shaped exhaust tailpipes, polished aluminium exterior mirrors, an incredibly discreet rear spoiler and angular body-coloured lower door strips — along the outside of both the front and rear doors at sill level — are the only other indicators that this is no ordinary A4 saloon. A real Audi buff would, of course, also know that, like other Audi S models, the S4 can be ordered in a choice of exclusive paint finishes. Ours came in a vibrant Brilliant Red.

Inside, the stylishly low-key theme continues. The affluent cabin could only be Audi: ergonomically spot-on and boasting top quality materials and finish. More S quattro Series trademarks include electrically adjustable Recaro sports seats upholstered in black leather and a matching part-perforated leather three-spoke sports steering wheel crowned with the 'S' emblem and with sculpted cut-outs for your thumbs. It feels just right in your hands. Look down as you get in and you'll see more discreet S4 badges on the polished aluminium sill kick-plates.

A first-rate driving position offering excellent all-round visibility can be taken as read — thanks to the supportive, electrically-adjustable Recaro seat with its pull-out under-thigh cushion, a large range of height and reach adjustment for the steering column and the four-way electrically-adjustable lumbar support. The auto-dipping rear-view mirror can be turned on and off — not all auto-dim mirrors allow you to do this, but it is particularly helpful when you need to reverse at night. Six-stage heated seats are likewise a key ingredient of the comfort package. Clearly visible through the steering wheel's top arc are two large and two small dials for revs, speed, temp and fuel, all with crisp white graphics and polished satin chrome bezels.

Beautifully integrated brushed silver aluminium trim highlights jazz up the attractively all-black cabin (trim, upholstery, carpets and even the headlining). Attention to detail is extremely thorough and includes the ultra-slim chrome bezel topping off the gear-knob. The centre console houses the screen and amazingly straightforward controls for the BOSE sound system, navigation and TV/DVD as well as for the dual-zone air conditioning.

A neat switch integrated into the wiper stalk operates the driver's information system. Below the left-hand indicator stalk is another for the cruise control. There are a good number of stowage trays and cubbies and also useful drawers — one concealed under each of the front seats. There's no central armrest between the front seats, but that's a good thing because it leaves lots of room for your elbows during spirited driving! The good-sized glovebox is lockable and also accommodates the 6-CD autochanger. All four windows are one-shot up/down and there's 'move-off' central auto-locking and two-stage unlocking. Simple, convenient and secure.

The back doors open very wide — almost ninety degrees — for easy access. Rear seat passengers enjoy matching sports-shaped seats and space in the back is generous if the front seat occupants are under six feet tall. There's actually room for three, but it's so good for two adults with the large padded central armrest down that you probably wouldn't want to let a third person in!

The boot takes 460 litres of luggage (our test car swallowed two very large Samsonite cases and skiing gear) but with the split folding rear seats lowered you can load 720 litres. A 'ski-hatch' adds extra flexibility. There are also two cut-out storage areas in the rear wings, ideal for soft bags. If that's not enough, there's plenty of room for oddments inside the eight-inch-deep upturned full-size spare wheel under the boot floor. Alongside the spare you'll find two neat tool kits, one of which contains the jack. Accurate rear parking sensors make light work of parking, day or night.

Which brings us neatly back to that V8 squeezed under the bonnet. The S4's powerplant is notable for more than its devilishly eager 339bhp. And just as impressive is the story of how it got there in the first place.

To make it compact enough to fit into an A4 engine bay, Audi's engine development team had to re-engineer the chain drive for the camshafts and ancillaries, which resulted in an engine length reduction of 52mm to just 464mm. In the process, they even managed to shave some weight by lightening the pistons and connecting rods. Not only does this make for low frictional losses in the engine and a high maximum engine speed of 7,200rpm, but it also contributes to a total engine weight of just 195kg. Not only that, but it looks magnificent, too.

The result is an ultra-compact five-valve-per-cylinder 4.2-litre V8 with exceptional power: it pumps out 339bhp at 7,000rpm and 302lb ft of torque at 3,500rpm. And even at just 1,100rpm the V8 produces almost 221lb ft, while between 3,000 and just under 4,500rpm the peak-torque range is always above 295lb ft. So, the S4 gives you a massive torque spread. Get it alone on your favourite back road and you could — although you wouldn't — slot the lever into 4th and leave it there, such is the V8's terrific tractability.

Another first for the S4 is that its V8 comes paired as standard with a purpose-built six-speed manual gearbox operated via a short-throw gearlever. Fire up the engine and the fun begins. Even at tickover, there's an intimidating edge to the V8. Not loud; just a tuneful, unmistakable eight-cylinder burble laden with promise. Blip the throttle and it feels instantly alert as the needle sprints round the rev-counter towards the 7,000rpm red-line. Slip the lever into first gear. The gate is positive and the throw well-weighted, so there's never any doubt about the gear you've selected. Now nose away from the kerb.

Such is the torque that the S4 could just as easily have moved off in second. It doesn't take long to realise that this V8 is a great powerplant. No longer than it takes you to find a 'good' road. Honest, too: no turbo or supercharger to boost the power — just good old-fashioned cubic inches. Sorry, cubic centimetres. In fact, whatever gear you're in, push the accelerator pedal — throttle response is instant — all the way to the floor, and the S4 takes off like a scalded cat. Do this in the lower gears and progress is brutal; even in the higher gears the shove in the back is relentless.

At this point you'll be glad you have quattro all-wheel drive. The S4's self-tracking trapezoidal-link rear axle has been specially designed for quattro drive. The quattro system uses a self-locking Torsen centre differential to distribute drive between the front and rear axles in keeping with the prevailing 'grip' conditions. Combined with a chassis lowered by 20mm compared to standard models, and the extensive use of aluminium for the suspension (with a resultant lower unsprung weight), this guarantees excellent traction and outstanding roadholding — whatever the weather conditions — along with superb straight-line running and high-speed directional stability.

And it also ensures that you can get down every last ounce of power. Interestingly, despite some appropriately seasonal wet and mucky weather during our week's testing, the S4's stability control warning light barely flickered. This really is an amazingly manageable machine considering just how much power is at your disposal.

Another beneficiary of the S4's lightweight aluminium set-up and reduced unsprung weight is the Servotronic speed-sensitive steering. This uses a 'sharper' rack than the standard A4 and up to about 45-ish mph it's a little on the light side. But it's precise. Get past that and it's well-weighted and direct. The low unsprung masses also benefit the ride comfort, which is firmly on the comfortable side of firm.

Refinement is one of the S4's strong points. Despite a delightfully aggressive snarling soundtrack under hard acceleration, at cruising speeds it ebbs back to a soothingly deep purr. Motorway driving is totally effortless — 70mph calling for just 1,850rpm in 6th gear — and journeys feel noticeably shorter than the actual miles travelled.

The marvellously comfortable leather Recaro seats help, but much of the smoothness is down to the S4's heart. The creamy V8. The nicest thing about the S4 is that however refined it appears, it takes but a flex of your right foot to rouse it from a happy-go-lucky loping motorway pace and send your adrenaline levels into overdrive. Which is precisely what Audi intended when it built it: a car that will take you comfortably from A to B, or a car that will thrill you in comfort from A to B. And the choice is always yours for the choosing.

Handling is, in a word, unflappable. The S4 is a seriously fast car. Not only do you appreciate the quattro's tenacious grip when getting off the line, but it allows you to corner at speeds likely to leave other super-saloon drivers white knuckled as they try to keep up. Balance is very good, and shows at its best in long, fast sweeping bends. Wherever you are and whatever the weather, behind the wheel of the S4 you will feel and be safe. And — as long as you don't do anything downright foolish — so will your passengers.

Going fast is not very clever if you can't also stop fast. The S4 does both extremely well. With large vented discs (340mm front/300mm rear) at each corner backed up by ABS, Electronic Brake-force Distribution and Audi's Electronic Stabilisation Program, braking is first-class and pedal feel progressive, allowing smooth modulation. The S4 also benefits from a new dual-rate servo. For comfort braking (low to medium retardation) this provides a firm feel at the brake pedal for good control.

But push harder, for full deceleration, and the ratio of foot pressure to stopping power more than doubles so that you get far greater retardation for less distance travelled by the pedal. In short, full-on braking requires less effort for proportionally more stopping power and with less pedal travel than on a conventional system. The ESP also features improved understeer control and a brake disc wipe function for optimum wet weather braking.

As we've come to expect from Audi, there's a full complement of safety equipment including two-stage front airbags, side airbags integrated into the seat backs and Audi's SIDEGUARD head airbag system which covers the entire side window area and the A-pillars. Additionally there's quattro permanent four-wheel drive, anti-whiplash active head restraints for the Recaro sports seats, a third rear headrest and shoulder/lap belt, heated windscreen washers and powerful xenon headlights.

Despite the outstanding performance, the S4's fuel economy remains more than acceptable. Our overall test figure came out to 21mpg — almost a perfect match with Audi's official combined figure of 21.2. Longish motorway runs also saw close to the official 28.8mpg figure registering on the on-board computer display.

Not as hardcore as the RS4, the S4 is nonetheless a very desirable piece of equipment. As a sporting saloon, it ticks all the boxes for those looking for an entertaining drive. Yet it will, and with charming grace, play the luxury tourer for you and three passengers for that weekend trip to Le Mans. Equally, it's just as practical helping out with the weekly shop. Add to that its all-weather ability and you have that rare companion — a car with attitude that's also got everything.

Audi S4 quattro | £37,115 Maximum speed: 155mph | 0-62mph: 5.6 seconds Test MPG: 21mpg | Power: 339bhp | Torque: 302lb ft Visit Audi's website