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Ingolstadt's new electric turbo technology produces stunning performance, potentially paving the way for a sporty diesel RS production model

Our Verdict

Audi RS5 coupé
The hottest 444bhp version of the A5 coupé range closes in on the BMW M3

The Audi RS5 is a success not only as a premium sports coupé, but as a long-distance cruiser offering an engaging drive.

What is it?

A late-stage prototype Audi RS5, fitted with a very potent ‘e-boost’ version of the next-generation Audi 3.0-litre V6 two-stage turbodiesel engine.

The new engine weighs 192kg, somewhat lighter than the previous version, and will arrive first this summer in the newly facelifted A6 and A7 in 215bhp and 268bhp forms. This 380bhp prototype, however, is expected to go into production next year, possibly as the first-ever Audi RS diesel.

Like many of today’s higher-end diesel engines, the new unit uses two-stage turbocharging. The smaller of the two is lighter and easier to spin up, and is intended to give the engine more grunt at lower engine speeds. The bigger turbo takes over at higher speeds.

The engine we’ve driven here is, however, something of a landmark design in that it uses electrical assistance to ensure that the smaller of the two turbochargers is spinning quickly enough to be active even at very low engine speeds.

In simple terms, Audi engineers have added an electrically powered blower to the engine’s induction system, which, at very low engine speeds, forces air into the induction system, spinning the smaller turbo into life.

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.

It is also likely to appear in RS form thanks to the fact that the ‘diesel-ness’ of this unit has been almost entirely eliminated, thanks to a combination of e-boosting, its pretty free-revving nature and the artificial sound generation of the exhaust system.

The question that hasn’t yet been answered is why RS customers – who presumably are not too sensitive to petrol prices – would want to buy a diesel-powered car. The Audi engineers I spoke to are still very bullish on the future of diesel and suggest that oil-burning is still the supreme motive power for long distance, high-speed, motorway journeys and cross-continental drives.

Moreover, after winning Le Mans with diesel powered sports cars, Audi finally has a diesel engine good enough to put in a future R8.

Audi RS5 V6 TDI-e prototype

Price na; 0-62mph ‘under 4secs’; Top speed 174mph (limited); Economy n/a; CO2 n/a g/km; Kerb weight n/a; Engine V6, 2967cc, twin turbocharged with electric booster; Power 380bhp at 4200rpm; Torque 553lb ft at 1250-2000rpm; Gearbox 8-spd torque converter automatic

Join the debate

Comments
17

28 May 2014

Not a fan of Audi (to say the least) but this new turbo sounds fantastic. I assume it can be used in a variety of different ways not just in a high performance diesel?

28 May 2014

... this turbo tech should work like a charm as well for small capacity petrol engines, that can feel wee bit flat below 2000 rpm. enabling them to pull still higher gearing reducing emissions still further as well as consumption.

28 May 2014

What a great idea. Hope to see it across the range soon, including in the Cayenne!

28 May 2014

Love this. The RS5 is very stealth, doesn't look much different to the normal version to the untrained eye.

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!

28 May 2014

VAG engines it will be unreliable, and prone failing completely but of course they will deny there is a problem with it..

28 May 2014

The unanswered question is not "why would a buyer of an expensive car choose diesel as surely the purchaser has enough money to afford the petrol?" but the opposite.
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.

maxecat

28 May 2014

Completely disgusting idea. One of these days the scales will fall from the eyes. Tell me a single 'heroic' diesel from any version of the past. Except the Massey 135.

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.

28 May 2014

Now, if they could only attach the steering wheel to the front wheels,then it might be ok!

Peter Cavellini.

28 May 2014

but I can't help asking why don't they apply this technology to petrol engines? All the dim-wits who keep swooning over diesel torque conveniently forget that this effortless performance has less to do with this fuel and more with the turbocharging. There's no reason why bi-turbo or e-turbo petrol engines won't beat the diesel engines, except perhaps in high-milers. (Take Ford's 1L for instance).
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.

28 May 2014

HH, I could be mistaken here but I've got an F30 335d xDrive and I'm pretty sure that it too has twin turbo with electric charger induction? It's not exactly pedestrian with its 313hp but Alpina seem to be able to tweek about 345hp out of it and I'm sure that in "prototype" guise it could touch 380bhp. Are Audi disguising catch-up as a revolution or have I been listening to too much BMW sales waffle?

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