Last week we drove Volvo’s 2.0 TDI engine in the S60 D4, the first sub-100 g/km saloon car in its sector. Audi’s powertrain response has arrived in the form of the new A6 TDI ultra, which cuts CO2 emissions by up to 14 per cent and brings it bang into contention with Volvo’s similarly sized S80.

The new A6 TDI ultra gains another 13 bhp (now 187bhp) and matches Volvo with a peak torque of 400Nm (295 lb-ft).

As with other engines in its class, Audi’s new 2.0 TDI is EU6-compliant, making it future proofed up to around 2017.

Audi claims it’s the “most cost effective conventionally powered car in the premium executive class”, based on a combined fuel economy of 64.2 mph, a CO2 output of 114g/km and Benefit-in-Kind (BIK) tax duty of 17% (down from 21% in its predecessor).

The A6 TDI ultra is priced from £32,515, accelerates from 0 to 62mph in 8.2 seconds and can reach a top speed of 144mph.

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Audi’s frugal new 187bhp TDI power unit is available in both A6 Saloon and Avant models.

By comparison Volvo’s 8-speed Geartronic S80 D4 SE Lux, as fitted with its new Drive-E powertrain, is priced from £33,720, accelerates from 0 to 62mph in 7.9 seconds and reaches a top speed of 140mph. It offers a fuel economy of 65.7 mpg, a CO2 output of 113g/km and a BIK of 15% (or 18% in Executive specification).

Looks like Audi’s ‘most cost effective’ claim might need a slight tweak.

At launch Audi’s A6 ultra is fitted with a completely redesigned seven-speed S tronic twin-clutch transmission, which replaces the eight-speed multitronic CVT used in previous four-cylinder models. A manual box will be offered later in 2014.

Audi’s super-frugal power unit can be paired with SE, S line or Black Edition specifications – bringing with it 20-inch alloy wheels which no doubt destroy some of those efficiency gains.

An A6 Avant TDI ultra is also available, with CO2 emissions of 119 g/Km, while the new engine will also find its way into the A4, A5 Coupé and A5 Sportback with CO2 emissions down to just 104g/km.