This ‘e-booster’ is connected to the engine’s intercooler on one side and to the induction system on the other, pushing air through the smaller turbocharger impeller between start-up and 3000rpm. At higher speeds, the e-booster is bypassed entirely.
The e-booster is also intended to keep the engine on boil on, say, twisty back roads. Typically with diesel engines, braking for a corner also slows the engine and bleeds off boost. This results in slower acceleration out of the same corner while the engine spins up enough to get the turbos back on boost.
But fitted with this new e-booster, the engine’s turbochargers can be primed while the driver is still braking, so that full torque is available virtually immediately the driver gets back on the gas.
Although Audi engineers experimented with turbocharger units that were driven directly by an electric motor, they decided not to pursue the design because it resulted in extra inertia, which, ironically, slowed the turbocharger response times.
The e-booster is powered by its own 48v electrical system, while the rest of the car uses a conventional 12v electrical system.
What's it like?
As you might expect with 553lb ft of torque on tap from just 1250rpm, this Audi RS5 diesel is bombastically rapid.
We drove the car at Audi’s new short driver training circuit near Munich. While this was a long way from the open road, the track’s very tight curves, which demand a great deal of braking and re-acceleration, were ideal for testing out the ‘e-boost’ promise.
We followed a hot RS6 pace car – driven by a professional Audi driver – around the track in order to give us some idea of how this RS5 prototype can deal with Audi’s fastest RS road car.
From a standing start, the RS5 had the measure of the RS6 for the first couple of seconds, before the RS6 pulled away. There’s no doubt that that this engine gets away from rest very quickly indeed. But after that the wall of seamless torque never seems to let up.
Left in the automatic gearbox's ‘Sports’ mode, the engine never had a chance of revving out, not just because the transmission’s brain wouldn’t let it – there’s little point in trying with torque peaking at 2000rpm and power at 4200rpm.
Another part of the reason that the engine responds less like a diesel is that the crankshaft, conrods and pistons have all been redesigned to reduce weight. These reciprocating parts are a claimed 20kg lighter than normal. That’s a lot less mass to speed up and slow down.
The promise of massive pull being instantly on tap as you pull out of slow corners is absolutely upheld. On six quick-ish laps, the engine was never left floundering for instant pace. Indeed, this engine drives hard enough to have the torque-vectoring rear differential working right up to the point it has to let the rear wheels slide a little.
Though I’m sure purists will say the car’s dynamic performance is ‘artificial’, this Audi RS5 doesn’t understeer. The steering weight remains constant even under the hardest cornering and – importantly – it is relatively easy to drive very hard.
Should I buy one?
You can’t – yet. While the Audi engineers on hand during our test were tight-lipped, I’d expect this engine to be offered some time next year.
Join the debate
supermanuel
Not a fan of Audi (to say the
Einarbb
Nice ...
Cobnapint
Nice
bubble1982
I Want
I'd lose the stripe, de-badge it, and revel in the expression on the 911 drivers faces when they're smoked from (standing start, rolling start, motorway overtake) take your pick!
Citytiger
If its like other recent
Maxecat
H.H. is asking the wrong question.
Why choose an engine, petrol, that has less efficiency thereby increasing your fuel bills?
Having the ability/desire to spend these sums on a new car does not automatically mean you are willing to part with far more money in fuel costs, most of which the government gets in taxation, let alone the hassle of having to refuel more often with a petrol car.
Yer pays yer money and takes yer choice as the saying goes. Thank goodness we are, at the moment, still allowed any choice. Maybe in a few years it will be restricted to cars similar to the Google battery driverless cars in the new.
eseaton
RS Diesel
Tractor, trucks, vans, and then stop it. Nobody yearns for one. They are just told they have to have one, and then justify it subsequently.
The French and Italian car indutries have been killed by them and their utilitarian charmlessness.
A Fiat is meant to be driven by the scuff of its neck, and so once was a fast Peugeot. And then along came the rattllers.
Who seriously aspires to a Guilietta with that bloody aweful noise coming out of it?
Or whatever the feeble successor to the 205GTi is called these days. Ratttle, rattle, change up quick....
Start a diesel on a cold morning and tell me honestly that is not one of the worst noises man has yet created.
Peter Cavellini
Ho hum..........
fadyady
Diesel has a place in SUVs and high-milers
For over a decade, for some unfathomable reason, European car makers have been pushing diesel engines on to the unsuspecting buyers, misleading them with artificially low CO2 figures while making no mention at all of the other harmful emissions, and equally strangely, a remarkable number of journalists have been recommending diesel over petrol.
Tuffty
Sounds familiar
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