The range-topping Audi S4 saloon and Avant estate models will be offered with a 342bhp mild-hybrid turbocharged diesel V6 engine.

The new powertrain will match a 3.0-litre V6 TDI diesel with a 48V belt-driven starter motor end electrically powered compressor. As well as producing 342bhp, the system produces 516lb ft of torque, allowing the S4 saloon to achieve 0-62mph in 4.8 secs, with a limited top speed of 155mph. The Avant is 0.1sec slower to reach 62mph.

Both versions of the Mercedes-AMG C43 rival will retain Audi's quattro four-wheel-drive system and use an eight-speed automatic gearbox.

Audi lists a fuel consumption of 45.5mpg for the S4 saloon and 44.8mpg for the estate. CO2 emissions range from 161-163g/km and 164-164g/km CO2 respectively.

The mild hybrid diesel engine is the same as that recently introduced on the S5, S6 and S7 Sportback models, albeit in a moderately different state of tune, with 342bhp. It's the only engine that will be offered in the European market for those models, and it's likely that Audi will continue that trend with the S4, given the need to meet new WLTP tests and fleet emission targets.

Audi is currently preparing updated versions of the regular A4 saloon and Avant models, which have been spied testing with a number of styling tweaks and are likely to be revealed later this year.

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