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Audi tests electric turbo on TDI engine

RS5 concept is powered by a 3.0-litre biturbo V-6 diesel with an electric turbocharger

Published: July 23, 2014, 4:00 AM
Updated: October 10, 2014, 9:15 PM

Audi RS5 Electric Turbo

COPENHAGEN, Denmark - Turbocharging is a core component of Volkswagen/Audi's

TDI diesel engines. It also is becoming an increasingly common feature of today's gasoline powerplants, primarily because it permits use of smaller engines that offer reduced fuel consumption in normal use.

To compensate for their smaller size, the turbo provides a significant power boost for those occasions when it is needed, such as passing, hill-climbing or merging onto expressways.

One traditional downside of turbochargers, in either gasoline or diesel engines, has been what's often called "turbo lag" – the tendency for a delay in acceleration response until the turbo "spools up" to a speed sufficient to generate boost pressure.

The bigger the turbo, the more boost and power it can generate but the greater the potential for turbo lag as it takes longer to spool up. Another of the many Catch 22s that engineers routinely face!

To combat that lag tendency, Audi's newest TDI diesel engine – a 3.0-litre V-6 that will make its debut in the Audi A7 – will be offered in bi-turbo form, with a small turbo that spools up quickly when exhaust flow is low and a second, larger one to take over and work in parallel at higher speeds.

It's a best-of-both-worlds scenario that revealed no lag at all when I tested it briefly in an A7 on public roads at an event here to celebrate 25 years of TDI technology.

But engineers are never satisfied. Especially Audi's engineers, it seems.

For that reason, they're now testing a variation on the biturbo system that uses an electric motor to spin up the small turbine even more quickly than exhaust gases can do so – totally eliminating any trace of turbo lag.

I got to test it too, on a race track, in an Audi RS5 fitted with the new engine. Honestly, the seat of my pants is not sufficiently calibrated to say that I could tell the difference.

There was surely no lag! The RS5 concept launched with the same kind of fervour I remember from the big-block muscle cars of my youth – minus the wheelspin. It was a Quattro, of course.

It's just one more example of the lengths engineers will go to optimize every aspect of the driving experience. Don't be surprised to see an e-turbo diesel in Audi's production car lineup in the near future.