Audi wants to remind you that diesel still has a place in the world, and it's going to try to prove it by fitting a mild-hybrid V6 TDI engine, with 347hp and 700Nm of torque, to the updated S4...
In the Metal:
The first thing that you'll notice about the Audi S4 (and indeed the entire updated A4 line-up) is the new styling at the front. Audi says it has hardly left a panel of its mid-size saloon's exterior untouched and, while there are new segmented brake lights and some tweaks to the styling at the side, the most noticeable changes are at the front. There you will find a new, lower, wider, flatter 'singleframe' grille, as well as the distinctive vent cut into the leading edge of the bonnet, meant to evoke memories of those fabulous old Audi Quattro rally cars. There are new lights, and new bumpers too, and we'd probably call it really handsome if only Audi hadn't accidentally made it look so much like a Hyundai i40.
At least this high-performance S4 model manages to swerve the Hyundai comparison a little, thanks to having a more aggressive front bumper, puffed-up wheelarches and, in the case of our test car, some sunglasses-challenging 'Turbo Blue' paintwork.
Inside, the changes are slightly hard to spot if you're not familiar with the outgoing Audi A4. The overall style and architecture are the same, so the biggest news is the upgraded infotainment system. That now gets a 10.1-inch touchscreen and loses the old click-wheel controller for the MMI infotainment system - a loss that we shall mourn, as it made using the system far more intuitive. Still, the latest MMI tech is impressive and, if the A4 and S4's cabin looks a little less dramatic than its cousins, with their double-decker screens, it has the virtue of simplicity. On the infotainment menu are such things as a parking space finder and, in some markets, a traffic light communication system that gives you a target speed to drive at to make the next green light. The S4 also gets S-specific digital instruments in the usual 'Virtual Cockpit' TFT screen.
Rather more specific to the S4 is the engine. Against the run of fashion, and indeed possibly against the run of public opinion, this new medium hot A4 is fuelled by diesel. Audi will offer a V6 petrol S4 in other global markets, but Europe only gets the diesel version for now, and it's coming with both impressive tech and impressive performance figures.
Possibly helping mollify the diesel critics, this 3.0-litre V6 TDI engine is actually part of a mild hybrid powertrain, using a 48-volt system and a belt-driven starter/generator. There's also an electrically driven turbocharger, which spins-up super-quick at low engine speeds to try and eliminate turbo lag. Peak power is a relatively middling 347hp, but torque is a mountainous 700Nm, albeit delivered at a fairly lofty 2,500rpm. Audi claims that the 48-volt mild hybrid system - which only assists the engine and the car's electrical demand, never driving the car by itself - contributes 0.4 litres per 100km in fuel savings. Presumably, you'd have to drive it very gently to see that kind of saving...
You will not drive the S4 gently. Not, at least, once you've experienced the angry-mule kick of all that torque, parcelled out to the tarmac by quattro four-wheel drive. Despite the promises of the spec sheet, that electric turbo doesn't eliminate turbo lag, but it does reduce it to a barely noticeable level, and the shove that comes on stream from low down is truly remarkable. As you accelerate, it feels as if some hefty assailant is pushing you back, firmly, into that gorgeous high-backed bucket seat and, unlike most diesel engines, the thrust never seems to tail off, at least not within the confines of public road driving. The S4 TDI has more torque than the more powerful, more expensive Audi RS 4 V6 petrol turbo, so it's quite likely that in most on-road driving situations, this will be the faster car.
It doesn't, at least in isolation, seem to give much away to the RS 4 in handling terms, either. Yes, the chassis settings are less aggressive, so there's more body lean in corners, and a sense of weight on the nose that slows down your time-to-apex, but the trade-off is very good comfort levels, and an ability to calmly soak up broken tarmac. It's going to be a pretty hard car to beat when the 'all-rounder' score is totted up. Here, after all, is a sensible, roomy (ish) four-door Audi with a diesel engine that can potentially beat 45mpg if driven with care, has very good comfort and refinement, and yet has the sort of punch associated with 1990s Japanese rally homologation specials.
It also has delicious steering feel and weight, an entertaining (if not quite flawless) augmented engined sound generator, and hefty quality that oozes from every leather pore, every strand of carbon-fibre, in the cabin.
Diesel may be unfashionable, but - damn - it's still effective.
What you get for your Money:
Audi hasn't set a price for the S4 yet, but it could potentially be quite the bargain. With that diesel engine trimming the CO2 levels, and therefore the VRT cost, we reckon it'll clock in with a price tag of around €75,000 - not cheap, but a lot less than the €105,000 asked for the RS 4, and the S4 is barely any slower in real terms, and almost as engaging to drive.
The Audi S4 is the car to make you fall in love with diesel again. Is that a good thing, or a bad thing? Probably depends on who you listen to, but what's impossible to ignore is that there are few, if any, rivals that can punch this hard, turn this well, and yet not mug you when it comes time to refuel. Until the electric revolution is finally, truly, here, the S4 proves that diesel can still rule.