Audi S4 TDI Vs Mercedes-AMG C43: Can Diesel Beat Petrol?

The latest version of the Audi S4 is different from all of its predecessors. And no, I’m not just talking about the kind of fuel you have to pump into its tank. No - unlike every other S4, this one has a mission. It’s here to show us that diesel still has its uses. It’s here to show that oil-burners still have their place, even as the wider VW Group - whose actions led to the fuel being demonised in the first place - ploughs ahead with multi-billion-dollar electrification plans.

We’ve already driven the S4 in isolation, and compared to its immediate ancestor at least, it does stack up. The V6 in the old one was far too dull to justify a typical six-cylinder petrol fuel economy figure, so we’ll happily get on board with something that feels punchier and is just as quick, yet can be coaxed into returning 50mpg on a run. But how does it fare against a middleweight performance estate with something more interesting going on under the bonnet?

Conveniently, TeamCT is running a Mercedes-AMG C43 estate as a long-term test car, setting up the grand diesel vs petrol showdown we’ve been hankering after. And straight away, the Merc is highlighting what’s not so good about the Audi.

Having spent a lot of time in the semi-skimmed AMG C in the week leading up to this test, the power band of the Audi’s 3.0-litre twin-turbo V6 suddenly seems perilously narrow. And while the electric compressor - powered by a 48-volt mild-hybrid system - does do a good job of combatting lag, there is a noticeably longer pause when you get on the throttle here relative to the C43.

But there’s no doubting the performance. The S4 will happily pick up and sod off at a hilarious rate, and the eight-speed automatic gearbox does help you make the most of the useful bit of the rev range. Although I probably shouldn’t be, I’m even quite partial to the burbly noise made possible by the little vibrating thing stuffed in the exhaust. The right-hand tailpipes, though, can do one - they’re completely fake.

Stick it through a set of corners, and you do get some body roll, but nothing disastrous. Traction is, as you’d hope, very good, and if you poke it with a stick, the quattro all-wheel drive system will quite suddenly stick a load of power to the rear boots and give you a little rotation to play with.

In Comfort mode, the S4 rides more smoothly than the C43 when it is set thusly. In Dynamic, though, the reverse is true. The Audi struggles to settle, with the body jiggling around almost constantly. It’s hard to tell where you’re getting the benefit from this extra stiffness from the adaptive dampers - the Mercedes actually seems to lean a little less.

That’s not the only thing the C43 has over the S4. As already noted, its 3.0-litre petrol twin-turbo V6 is more responsive, and yes, in terms of noise, there’s no contest. There’s something pleasantly throaty about the noise emitted by the quad tailpipes, which are (near enough) real in this case. I have a lot of time for the naughty bullwhip cracks on each upshift, too. But it does seem slower than the Audi out in the real world, which is going to happen when there’s a 133lb ft torque gap between these two.

Although the useable chunk of the rev range is inevitably fatter here, Mercedes’ ageing V6 isn’t an engine set up for high-revving heroics. The nine-speed automatic gearbox shifts up at 6000rpm, and if you try and change gear beyond that in manual mode, you hit a soft limiter portion that makes it feel as though the car has given up on life.

Speaking of the auto ‘box, the nine-speed unit performs similarly to the eight-speed in the Audi, and that’s to say… fine. Here, though, you can get a fast getaway from a standstill without the car pausing for thought before setting off. The same can’t be said of the S4 - you’d better make sure that the gap between cars on the roundabout is a decent one before trying to set off.

In corners, the C43 feels more neutral, with a more gradual breakaway at the rear than in the S4. Both cars are similarly porky at around 1800kg, but it’s the Mercedes that handles the bulk better - you don’t get that sense of it becoming unwieldy when pushed hard as with the Audi. The steering isn’t amazing on either car, with the Audi being better judged in terms of weight, and the Mercedes a touch more consistent. We’ll call that one a draw.

But is there an overall winner? That’s harder to judge. When going from the Mercedes to the Audi, you do miss the drama the Mercedes’ six-cylinder petrol engine can provide. But having run the C43 for six months now, I can’t help but question whether that additional shoutiness is worth it when you struggle to scrape 30mpg on a long cruise.

That’s the problem with these middleweight fast saloons and coupes. If you’re really interested in performance, you are, as we’ve said before, probably better off stretching to the full-fat option. In this instance, the C63. In this territory, especially if you’re going to be clocking a lot of miles, the S4 makes a lot of sense. The 50 TDI that sits under the S4 is almost as quick for quite a bit less money, but the kudos of the S badge and the spangly bits will make that a non-issue for many.

Here, today, though, there’s no question that the C43 is the better performance car, and not just because of what’s under the bonnet - it has the superior chassis too. So, diesel has not - this time at least - beaten petrol. But derv has given unleaded something to worry about, and shown that yes, diesel still has its uses. Audi S4, you’ve accomplished your mission.