New Audi S4 2019 review

The S4’s switch to diesel power might seem to come at an odd time, but it’s a powertrain that’s a perfect match for the car’s character. Torquey, refined and frugal - especially considering the thumping performance on offer - it sits well with a car that’s relaxing to drive, comfortable and understated to look at. There are more exciting performance saloons out there, but there are few which will be so easy to live with every day.

This is the new Audi S4. Like the rest of the range, the subtle sports saloon (and estate) has been refreshed for 2019, with revised styling, improved lighting tech, and a faster, prettier infotainment setup. 

But the big change comes under the bonnet, where petrol makes way for diesel. The timing of the fuel switch might seem a bit weird for some, given that the public’s perception of diesel only looks to be going one way. But can the S4 do anything to restore a little pride in the black pump?

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The S4’s powertrain is the same as that used by recently launched S6; that means a 3.0-litre turbocharged V6 backed up by a 48-volt electrical system. Interestingly, Chinese and American markets keep the petrol S4, but as it stands in Europe, only the bookends of the S family - the S3 and S8 - are sticking with petrol for now.

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The 48 volt architecture enables a mild hybrid system, which features an integrated alternator starter and a compact 0.5kWh lithium-ion battery. Among other things, this drives an electric compressor installed between the intercooler and the engine which, according to Audi, effectively eliminates turbo lag. 

The result is 342bhp. While that’s slightly down on the old petrol, the peak torque figure is a whopping 700nm - up 200nm. And it can really be felt on the road: the S4 launches forward with a constant surge of acceleration right to the red line. The electric compressor achieves the desired job: there’s little in the way of turbo lag to hold it back, so means that it’s a fantastic tool for quick overtakes. You do need to be above 2,000rpm to feel the benefits though, as before the big turbo gets on boost, there’s a slight lull before the shove.

It even makes a decent noise, too. It’s not quite the tuneful note of the outgoing petrol, but the deep, big-lunged growl seems a good match for the heavy duty shove in the back. The eight speed gearbox shifts smoothly and is reasonably responsive in manual mode.

That torque also means that the S4 can actually feel about as playful as an Audi S car before or since. The optional Sport Differential is able to send power to the rear wheels individually, which means that on the exit of a tight corner, a deliberate hoof of the throttle will cause the back end to step out of line. For the most part, however, it just delivers phenomenal traction, firing the S4 from one corner to the next. The chassis itself has quite a neutral balance to it.

If only the steering could offer some sort of feedback, and the S4 would be a genuinely enjoyable. It’s very light - even in sport mode - so it doesn’t quite offer the feel to instil much confidence along a twisty road. The dynamic steering, which adjusts the rate of response according to road speed, is fairly intuitive though. 

But despite the largely positive news about the handling, a long cruise is the S4’s most natural gait. The suspension soaks up bumps pretty much as capably as a conventional A4, which means that, minor low-speed jiggle aside, it’s composed yet relaxing. Wind noise is minimal, road noise is reasonable, and the long-legged engine is barely audible at speed. In other words, it’s a phenomenal long-distance cruiser.

And the other benefit of that engine comes with fuel efficiency. The S4’s mild hybrid tech allows the stop/start system to engage near-instantly, and can cut the ignition from around 14mph to coast fuel-free up to traffic lights. At higher speeds, the coasting function allows for the engine to cut out for up 40 seconds if the system deems it to be the most efficient way of doing things. In practice, the start/stop system didn’t seem too keen to engage - it didn’t want to cut power while big energy draws like the air con system were running. 

Audi says that the system is able to save up to 0.4litres of fuel for every 100km driven. Not a staggering amount, but better than nothing. The result is 37.3mpg on the WLTP testing cycle - impressive for a car which will trouble most hot hatches in a straight line. 

Away from that powertrain, the 2019 S4 gains the same updates as the rest of the A4 family. That means that the outside gets reshaped headlights, a lower, wider grille, a reprofiled shoulder line along the sides, and a chrome strip which separates the touched-up tail lights. 19-inch alloy wheels are standard, as is a body kit which adds a subtle extra dose of muscle.

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The interior remains a lovely place to sit. The only real changes come with the tech: Audi’s Virtual Cockpit digital dials are sharper than before, and offer new menu layouts. The larger infotainment screen has grown in size to 10 inches, is now touch sensitive, and uses smartphone-style tiles for sub-menus.

With arguably its closest rival, the Mercedes-AMG C43, starting from £50,120, an entry point of £48,000 for the S4 Saloon (and £49,400 for the Avant) seems reasonably. Thats in standard trim, which comes with a long kit list itself, but there’s two further upgrade levels beyond it. For an extra £1,500, the Black Edition comes with a black styling pack which changes the exterior brightwork for darker trim. At the top of the range is the Vorsprung, which among other things, adds the quattro sport differential, a panoramic sunroof, a head-up display and a Bang & Olufsen sound system for the £60,850 asking price.