Audi S7 Sportback

Audi's S7 Sportback switches to diesel power. Jonathan Crouch takes a look.

The second generation Audi S7 Sportback packs a massive 700Nm punch from its 350PS TDI diesel engine: yes, for the first time in an S7, there's diesel power - and it's the only option. The car also gets an eight-speed tiptronic transmission, quattro four wheel drive, adaptive damping and virtually all of the brand's latest performance technology into a practical but exclusively styled five-door coupe-style silhouette. It's a rare and tempting proposition for the money being asked.

It wasn't very long ago that a car like this simply wouldn't have been possible. Ferrari-style pulling power stats, with five-door family versatility. Vanishingly rare exclusivity and a hand-built interior for less than £70,000. And, most tellingly, rest to sixty two mph in just five seconds, yet a 35mpg WLTP-rated capability. Welcome to the second generation Audi S7 Sportback. This, as you may already have guessed, is a performance flagship for the A7 Sportback range, this a 'five-door coupe' model line that Ingolstadt has created to challenge stylised executive contenders like BMW's 8 Series GranCoupe and the Mercedes CLS. I say 'a performance flagship': actually 'the' performance flagship of the A7 range is the 600PS RS 7 Sportback model, a car which looks tempting but costs vastly more than this S7 and also costs vastly more to run because it uses a V8 biturbo petrol engine to go, well, not all that much faster.

The 3.0-litre V6 TDI engine used here with its electrically-powered compressor is basically the unit originally introduced in Audi's SQ7 large SUV, but has been embellished here with a 48-volt electrical system, which has taken the powerplant's total power output to 350PS. All of those braked horses are transmitted via an eight-speed tiptronic automatic transmission to the car's quattro all-wheel-drive system. The electrically powered compressor is the major reason for this S7 Sportback model's startling performance. 62mph from rest takes just 5.1s - which is virtually the same as was achieved by the far more powerful 4.0-litre petrol V8 of the previous generation model. And you get that performance here with far more pulling power this time round thanks to dual supercharging that sees the electrically powered compressor working in tandem with the exhaust turbocharger and producing 700Nm of torque. The standard-fit progressive steering comes with sports ratios in its basic configuration; the greater the steering lock, the more direct the steering is. There's also adaptive air suspension. And optional dynamic all-wheel steering which below 37mph, turns the rear wheels in the opposite direction to the fronts for a tighter turning circle. At over 37mph, the rears move slightly in the same direction as the fronts to aid stability. For even more dynamic road behaviour, the quattro 4WD system can be supplemented with an optional 'Sport differential' on the rear axle. This literally pushes the car into the bend, producing a high level of agility.

You'll buy this car because of what it says about its brand and because of what it says about you, with a look that's measured, efficient, sporting and quietly exclusive. The long bonnet, the long wheelbase and the short overhangs create perfect proportions, while the swooping roofline is reasonably successful in giving this five-door model the character of a coupe. Subtle, eye-catching details set the S7 apart from its humbler A7 stablemates. The wide, low Singleframe grille features lamellas in aluminium and a centre section in dark chrome matt. The air inlets are enlarged over those normally featuring on an A7, with very bold contours, and their honeycomb-structure inserts are finished in titanium black. The blade running through them is trimmed in gleaming aluminium, as are the exterior mirror housings. Features that distinguish this S7 from its S6 saloon counterpart include the funnels in the air inlets and the angular trim strips on the side sills. The cabin is as well appointed as you'd expect from a range-topping A7 Sportback model, with beautiful monogrammed leather sports seats, and an S-specific graphic layout for the standard-fit Audi Virtual Cockpit instrument binnacle digital display which here features a central rev counter. The back seat offers reasonable space for three adults, but much more comfortable room for two and you get a fold down centre armrest with storage and cup holders. Out back, in this five-door model there's a 535-litre boot, extendable to 1,390-litres.

Prices start at around £69,000 - which is around £9,000 than you'll pay for the mechanically identical S6 saloon. That's for the standard S7 variant. You can also specify a plusher 'S Vorsprung' level of trim - but it'll cost you: think in terms of around £18,000 more for that. On the standard model, there are lots of options. You're probably going to want to pay extra for the lovely 'S sport seats with their integrated headrests. And you can add in ventilation and massage features, along with top-end Valcona leather to the front chairs. As for dynamic stuff, well many S7 buyers will want to look at upgrading to dynamic all-wheel steering and the optional sport differential. If you're thinking of taking your S7 to a track day (it'd certainly be fun to dismay the circuit regulars in a diesel car), then you'll need to consider the optional six-piston ceramic braking system, replacing the standard steel discs. The ceramic set-up is made from light, abrasion-resistant carbon fibre with 400mm discs at the front and 370mm discs at the rear. The complete ceramic brake system weighs nine kilograms less than its steel counterpart, so it significantly reduces unsprung masses with the effect of further enhancing driving dynamics, especially when cornering.

While the electrically powered compressor boosts the performance, the mild-hybrid system of this car helps to improve fuel efficiency. The 48-volt MHEV set-up comprises a 'BAS' belt alternator starter and a lithium-ion battery with a capacity of 10Ah housed in the vehicle floor beneath the luggage compartment. The BAS is connected to the crankshaft. During deceleration it can recover up to 8kW of power, which it then stores in the lithium-ion battery. When the driver accelerates again, the BAS reacts instantly by restarting the engine. MHEV technology allows for start/stop operation from a speed as low as 13mph. Thanks in part to the integration of the mild-hybrid system and the vehicle sensors, the S models realize a fuel saving of up to 0.4 litres in real driving conditions and can coast for up to 40 seconds with the combustion engine deactivated. WLTP fuel economy values for the S7 TDI are quoted at 35.8mpg (or 35.3mpg for the Vorsprung' model), equating to NEDC-correlated CO2 emissions of 170g/km.

This second generation S7 Sportback is a model meriting a measured approach, a sporting car rather than a sports car, its blend of talents making it a mainstream A7 with a bit extra in hand rather than a hard-riding RS-style Audi that's been tuned back a couple of notches. That in itself is no bad thing. You'll enjoy the S7 for its smooth ride, its effortless torquey TDI engine, the astonishing technology and its slick-shifting transmission. In other words, you'll enjoy it very much. There are obviously more efficient fast executive five-doors and sharper ones to drive. But none that quite share this model's package of power, practicality and panache. And it's one of the new breed of large executive Audi S model cars that have more about them than simply a big engine up-front, a contender that might even surprise you if in the past, you've limited your options with cars like this to brands like BMW and Porsche. Above all, it's a mature car, one that doesn't have to try too hard, a model that creeps in under the radar. Very desirable, very rare and very, very Audi.