It's amazing to think how far diesel engines have moved on in the last 20 years, but Audi is proving there’s still lots more to come. Under the bonnet of this prototype A6 saloon is a new diesel engine based on the familiar 3.0-litre V6 Biturbo that uses an electric turbocharger in a bid to eliminate lag altogether.
Normally in the Biturbo, exhaust gases are used to spool up a small turbo which fills the gap in torque that comes at low revs when you floor the throttle. When enough exhaust gases are coming from the engine, a larger turbo kicks in. It’s effective to a point, but this new set-up is a far better proposition.
Instead of relying on exhaust gases, the smaller turbo here is electrically driven and will already be spooled up from a standstill and at low speeds. The effect, as we found out, is neck-snapping acceleration off the line. The standard A6 Biturbo covers 0-62mph in 5.1 seconds, and while Audi couldn’t give us a specific time, engineers did tell us the electric turbo version was two car lengths ahead after just three seconds.
The switchover between the electric and traditional turbos is almost seamless, with only a slight dip in acceleration that should be ironed out when this engine reaches production. Engineers need to work on making it more fuel efficient, too – as it stands it’s thirstier than the traditional Biturbo.
Audi couldn’t tell us when this engine will grace a production car, but the technology doesn’t seem too far away. We’d bet on it being offered as a top-spec option in the next-generation A4.
And with instant responses, a growling engine note and blistering acceleration, a diesel sports car is almost certainly in Audi’s future.