Understated almost to the point of anonymity, the S4 is the mid-level performance version of the Audi A4 saloon. Swapping between twin-turbocharged, supercharged V6 and even a naturally aspirated V8 engine in times gone by, the B9 S4 returned to a single-turbocharged 3-litre V6, combined with an eight-speed automatic transmission and the ubiquitous quattro all-wheel drive.
That, however, is about to change, as the S4’s successor will eschew its petrol V6 for the new mild-hybrid V6 diesel for the first time. The petrol S4 isn’t leaving behind an empty market niche either, as both the Mercedes-AMG C43, and in the near future BMW’s all-new G20 M340i, will fill the void.
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The petrol S4’s combination of a smooth, punchy, petrol powertrain, svelte styling and exceptional build quality still make it a desirable mid-level performance saloon though, and has left a sizable void for the new S4 TDI to fill.
Engine, performance and 0-60 time
The previous S4’s 3-litre single-turbo petrol V6 is one still used throughout the Audi range. Available in A6, A7 and A8 models, not to mention in various Porsches and even Bentley’s plug-in hybrid Bentayga, it’s a refined, if not particularly sporty unit. In the B9 S4, it’s good for 349bhp at 5400-6400rpm and 369lb ft from 1370 to 4500rpm.
Performance is about where one might expect, with both saloon and estate slipping under the 5.0sec to 62mph barrier (4.7 and 4.9sec respectively). Top speed is a limited 155mph. It may lack the exotic flare of a naturally aspirated V8, and the instant punch of the previous B8 S4’s supercharged V6, but the unit here finds a more artful balance between brisk performance and not being able to achieve more than 30mpg on any given day.
The biggest news on the B9 S4’s launch was the switch from supercharged to turbocharged technology, plus the adoption of an eight-speed automatic gearbox instead of the previous car’s dual-clutch S-tronic transmission. The S4 and S4 Avant are around 75kg less than the previous S4s too, at 1630 and 1675kg respectively.
The S4 is, of course, underpinned by a four-wheel-drive chassis. Under normal circumstances power is split 40/60 front to rear, but up to 70 per cent of power can go to the front axle or 85 per cent to the rear should conditions demand it. The active torque vectoring ‘sport differential’ for the rear axle remains an option at around £1500 and the new S4 also lightly brakes the inside wheels during hard cornering to create a more agile feeling. Also on the options list is Continuous Damper Control, which features Comfort, Auto and Dynamic settings, and the variable-ratio Dynamic Steering system.
What’s it like to drive?
The first thing that strikes you about the S4 is how refined it is. Our car is fully loaded with 19-inch wheels, Continuous Damper Control and the clever sport differential. It rides beautifully in Comfort mode and on our admittedly smooth-surfaced test route, Dynamic mode does little to ruffle the fluid composure of the car. Allied to the almost invisible eight-speed automatic and instantly responsive engine, the S4 makes effortless progress.
The dynamic steering system is worlds better than before, but still has an initial jumpiness that feels slightly odd and it’s so light that you don’t feel there’s a real connection to the front wheels. Having said that it takes only a few minutes to adapt to that and the rate of response feels much more natural and consistent than those hateful early systems. I’m still not sold on the whole concept but I’ll admit it’s not a huge issue in this car.
As for the chassis, it’s partly brilliant and partly disappointing. The ride really is fluid and allows you to build up a nice, easy rhythm, and whilst there’s quite a bit of body roll the car has a sense of effortless control that seems to fit with its easy-going but impressive turn of speed. The balance is also pretty good. Of course, it can be made to understeer if you don’t listen to the howling tyres (it comes as standard with Hankooks, which are brilliant in the wet but lack response and mid-corner grip in the dry), but if you turn the car in slightly slower and then commit to the throttle you feel the sport diff sending power to the outside rear tyre. As the corner unfolds a small yaw angle builds and then stabilises, so you exit each corner with the car driving forwards but held in a shallow oversteering angle. It’s actually a really cool sensation.
The only problem is that the S4 feels slightly too soft-edged. The chassis is clearly very well sorted, the balance with the sport diff is adjustable and not relentlessly understeery, but the weight savings advertised don’t really make themselves felt. Instead of feeling lithe and agile the S4 too often feels like you’re coercing it into revealing its sportier side. I’m not suggesting it should be crashy and edgy, but a small increase in body control and turn-in response, a bit more volume for the exhaust and sharper gearshifts would transform the car. At the moment is feels too often just like a ‘normal’ A4 that just happens to have a load more performance, rather than a true performance derivative. It should be said that the S4 saloon is tangibly more agile than the Avant model and feels slightly keener to entertain.
It’s always tempting to suggest that the estate version of any fast Audi is the one to have. Audi has such a rich heritage in fast estates, from the Porsche-engineered RS2 to original RS4 and now with the massively potent RS6 Avant. However, in the case of the S4 the five-door version isn’t quite as much fun as the saloon. The weight difference isn’t huge at 45kg (1675 versus 1630kg) but you can definitely feel it. It’s slightly slower to change direction and although we’re talking small degrees here, the saloon car just has cleaner reactions and a slight advantage in terms of agility.
Of course, the Avant has its advantages. It’s just as understated as the saloon but has that estate car cool that fits nicely with the discreet nature of the S4, and it’s, um, got a bigger boot. I suspect the former might be what swings it for many buyers and I can hardly blame them. However, if you want the very best S4 in dynamic terms you should stick to the saloon car. It’s tangibly sharper and feels keener to be driven with enthusiasm.
Price and rivals
The B9 S4 was taken off-sale during the sweeping WLTP reforms that forced many models to do the same at the end of 2018. Rather than go through the motions of re-certifying a new petrol version before the A4’s range-wide update, Audi has instead left it off-sale until the facelifted version arrives with, as mentioned before, a high-performance V6 diesel engine.
If you’re still interested in a compact executive with a potent petrol six-cylinder engine, both Mercedes and BMW are more than willing. The Mercedes-AMG C43 has just undergone a recent refresh, helping keep the ageing C-class up to date thanks to some interior styling changes. The C43 is no halfway-house performance car on the road either, with an impressive combination of outright punch and theatre from its 3-litre turbocharged V6 engine. It drives well too, with a more discernible edge to its dynamic package.
BMW’s incoming M340i M Performance model will also lay claim to this battleground, powered here with a 376bhp 3-litre turbocharged in-line six borrowed from the X3 M40i. UK prices and final specifications have yet to be revealed, but should fall in line with the C43 at around £50k.