Audi has continued its run of converting S models to diesel with the new S4 and S4 Avant.
The compact saloon and its always cooler wagon brother will both come with the same 342bhp mild hybrid diesel engine that has already been dropped into the S5, the S6 and S7 solely for European markets.
Thanks to the electric generator/motor’s assistance the 3.0-litre V6 diesel – an Audi staple for years – has to work less hard and can therefore be more efficient. It harvests otherwise wasted energy under deceleration and sends it to a 48v battery that can then supply the motor with power when the driver gets back on the right-hand pedal.
There are only two pedals: the S4 will only use a specially-adapted eight-speed Tiptronic automatic that has extra software to cope with the mild hybrid’s extended functionality versus a stop-start setup. The engine will cut out when speeds drop to 13mph. Quattro all-wheel drive is standard as well, naturally.
Fuel economy is listed under WLTP testing as an achievable-sounding 45.5mpg for the saloon and 44.8mpg for the Avant. Far more interesting is the 516lb ft of torque on tap. In tandem with tall gearing it could make the diesel S4 a seriously rapid cross-country machine.
As for acceleration stats, the saloon will launch to 62mph in 4.8 seconds while the Avant takes a negligible tenth of a second longer.
We expect the next S3 to continue using the EA888 four-cylinder petrol engine; the V6 diesel won’t fit and the ever-evolving petrol lump is relatively efficient anyway. An updated version of the flagship S8 has yet to be revealed, though, and it will be interesting to see whether Audi goes diesel with that.
Historically the always-petrol S4 began life as the 1991 100 S4, which had a turbocharged 20-valve five-cylinder of 2.2 litres. It threw 227bhp at all four wheels and was joined in 1992 in some markets by an S4 Plus, which had an aluminium 4.2-litre V8 with 276bhp. New models switched to a twin-turbo 2.7-litre V6, then a normally-aspirated 4.2-litre V8, a 3.0-litre supercharged V6 and a turbocharged 3.0-litre V6 before the S range’s move to diesel.