Bestowed with the title of Audi’s most powerful production diesel engine yet, this twin-turbo 3.0 litre V6 was put into service on the British-market A6 and A7 models at the start of the year, heading the diesel vehicle line-up, while the first oil-burning S model – the SQ5 TDI – debuted with the engine in June.
And now that Porsche and Volkswagen are more involved than ever, we guess ‘Diesel S’ variants of the former’s popular Panamera and Cayenne models, powered by this engine, may one day come to fruition.
What’s so special about this motor? Well, apart from featuring dual-stage, series-sequential turbocharging, it employs a sound actuator (basically a speaker) in the exhaust system’s auxiliary channel that “imposes a defined oscillation pattern on the exhaust flow and transforms the typical TDI exhaust note into a more sonorous roar that is closer to the output of a high-performance petrol engine.” Er… perhaps listening to it might help – it’s a very satisfying burble indeed:
The engine is based on Volkswagen’s single-turbo 3.0 litre TDI V6, variations of which range from 204-239 PS and 400-500 Nm of torque depending on the model. What the engineers did was add another turbocharger, tweak boost and fuel injection, and the figures leapt to 313 PS and 650 Nm. Max torque is available from just 1,500 rpm and max engine speed is 5,200 rpm.
So it packs more muscle, but the overall compression ratio has actually been decreased (from 16.8 to 16.0) via changes to the piston crown geometry. This helps to reduce harmful emissions.
Bolting two blowers on a V engine isn’t as straightforward as you might suppose – it’s a wide engine so they have to be placed at the back, with the smaller turbo mounted transversely and the bigger one longitudinally.
The smaller turbo, which uses a Honeywell system featuring variable turbine geometry, operates alone below 2,300 rpm. The two turbos work together in series from there on up to 3,400 rpm, when the bigger turbo supplies all the boost. Max power then comes in at 3,900 rpm.
As a direct result of all this, the A6 3.0 BiTDI quattro (Avant version pictured) does the century dash in just over 5 seconds and is capable of returning 6.4 litres per 100 km.
Up in the clouds, Rudolf Diesel is smiling.