What is it?
It doesn’t seem all that long ago that the Audi S4 was powered by a 4.2-litre, 339bhp V8. In fact, it wasn’t all that long ago that all of Audi’s S-badged models seemed to be using engines that would look preposterous by today’s standards. Just look at the old C6-generation S6; that had a massive 5.2-litre, 429bhp Lamborghini-derived V10 at its nose, and even then it wasn’t the fastest or most powerful version you could buy at the time.
How times have changed. These beguiling engines have now largely disappeared from Audi’s range of S cars, and even some of the ‘halo’ RS models have been shorn of a few cylinders. Take the current RS4 and RS5, for instance - in a previous life, both of these cars were champions of the naturally aspirated V8. Now, not so much.
That, however, is the way of the world. Attitudes change and priorities shift - and cars will inevitably change along with them. That’s why, under the bonnet of this new S4, you’ll find a 3.0-litre V6 diesel engine supplemented by a 48V mild-hybrid system, as opposed to a revised version of its predecessor’s 3.0-litre V6 petrol. It’s a move we’ve seen Audi make with updated versions of its other S-badged models too: the new S6 and S7 are now all fuelled from the black pump; while the recently launched SQ8 makes use of the 4.0-litre V8 diesel that will also appear in the soon-to-be-reintroduced SQ7. All of those cars feature some form of mild-hybridisation, too. The recently announced S8 seems to be the only new S-model to retain a heavy-hitting petrol motor, in European markets anyway.
Given the air of negativity that has surrounded oil-burning motors since the Dieselgate scandal broke back in 2015, Audi’s decision to redefine its middleweight performance range as it has is a bit of an eyebrow-raiser. One engineer said the move was based on the fact there’s still a strong level of demand for used examples of the first-generation SQ5 - which was the first Audi S model to feature a diesel motor, remember. Supposedly customers love the blend of performance and economy they offer, so the decision was made to roll similar engines out across the wider range.
While this might certainly be a contributing factor, I’m not sure it’s the sole reason. Tightening emissions regulations must have something to do with it. And considering cars such as the RS4 and RS5 now make use of smaller engines than they were a few generations ago, perhaps diesel is a way of further differentiating these halo products from the lower-order S cars.