It may be difficult to predict exactly how much appetite the UK’s sports saloon faithful currently has for the fast, diesel-engined four-door.

Some manufacturers clearly think it’s so meagre as to justify the early removal of derivatives and the cancellation of development programmes; some, but not all. And perhaps it’s appropriate that, having had such a significant hand in the scandal that did so much damage to the reputation of diesel engine technology back in 2015, Audi should now be the company doing what it can to restore that reputation.

As the Ingolstadt firm announced earlier in 2019, all future S-badged go-faster Audi models in Europe, bar one or two, are now to come with diesel engines intended to be equally big on torque and accessible for pace as they are fuel efficient and long striding in real-world use. Some, like the SQ-tagged performance SUVs, already were diesels, of course; but for Audi’s longer-lived and more celebrated quattro-driven sports saloons – one of which, in its latest guise, is this week’s test subject – that’s a major development.

So what will diesel power mean, exactly, for this heavily facelifted sixth-generation S4 aside from the addition of a TDI naming suffix?

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The best way to sum it up in headline terms may be to record that it has as much torque as the maddest Mercedes-AMG C63 super-saloon – but it is also rated for better than 40mpg on the latest WLTP combined fuel economy lab tests, offers twice as many driven wheels as the Merc and yet can be bought for two-thirds of the price.

Predictably, though, this new-groove, all-paw fast Audi relies on a very wide-ranging selection of the latest powertrain technologies to achieve what it does, which we’re about to lay out in detail.

The Audi S4 line-up at a glance

The S4 will still be available with a petrol engine in markets other than ours, but it’s a 342bhp V6 diesel or nothing in the UK. However, as before, there’s still a choice of saloon or Avant estate bodystyles. At present, the S4 TDI is available in both standard and Black Edition trim levels, although a range-topping Vorsprung model will join the line-up later this year.

Price £48,000 Power 342bhp Torque 516lb ft 0-60mph 4.6sec 30-70mph in fourth 5.2sec Fuel economy 29.1mpg CO2 emissions 164g/km 70-0mph 46.9m

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Audi S4

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