Tuesday 22nd July 2014

Audi RS5 TDI: Driven

Yes, you read that right - 'RS5 TDI'; PH drives Audi's intriguing TDI with motor-assisted turbocharging

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Would you buy a diesel powered Audi RS, BMW M-car or Merc AMG? Our instant response would have been 'no, are you mad?', but a drive of an RS5 TDI prototype has prompted some back-pedalling.

Electric compressor can augment exhaust gases

Audi has embraced the black pump more wholeheartedly than its German rivals, and while that's great for the CO2-concious fleet customers that make up half of its UK sales, it has struggled to make diesel sexy, even with all those TDI Le Mans wins.

The RS5 TDI is a serious attempt bash away some of those 'weekday diesel, weekend petrol' prejudices. So serious in fact that we were told by Audi's head of engineering, Ulrich Hackenberg, that there was a good chance it will be built.

Back in black
The car uses the same three-litre V6, twin-turbo TDI as used in the SQ5 but with the addition of an electric compressor to boost power from 313hp to 385hp. That's not far of the 450hp made by the V8 petrol RS5 but the diesel's peak torque of 553lb ft soundly beats the petrol car's 317lb ft. Audi claims a 0-62 time of around four seconds for the concept, compared to 4.5 for the standard petrol.

You'd never guess how ... oh, yes you will

The big jump is thanks to what will inevitably be called an electric turbo, but is really an electric compressor (or e-booster in Audi speak) that forces air to spin up the first of the two turbos. This happens in milliseconds according to Audi, and accounts for the fact that peak torque is now as low as 1,250rpm.

It brings a new definition of 'zero turbo lag'. We drove the concept briefly round a small track in Sweden (Sturup, near Malmo if anyone's interested) and the chief memory is one of truly addictive, medicine-ball-to-the-head acceleration. Audi supplied an RS6 Avant (0-62, 3.9 seconds) for short drag races and the TDI kept up until 50mph or so.

Anti lag
The car was fitted with an eight-speed slushbox with paddle shifters instead of the seven-speed dual-clutch in the V8 RS5 and flicking through the gears gave another demonstration of the power stab of the electric compressor, particularly when you lost revs. It essentially overcomes the extra weight of the TDI engine to get the revs up. Having eight speeds also meant there was somewhere to go when the lower redline was reached.

Production tech will debut on next-gen Q7

That extra weight, not just of the strengthened engine block, but also the flywheel and the stronger pistons and con-rods, is one drawback to getting diesels mentioned in the same breath as performance petrols. It takes more force to get them spinning and, if you come off the gas, the revs fall away more slowly. It's impossible to see diesel motors in track day weapons for example.

Then there's the noise. You knew we'd get there eventually. Audi has really worked on this aspect and the result here is admirable, if a little weird at times. All the work going into making TDIs more refined, driveable and economical, such as more pilot injections into the cylinder courtesy of ever higher fuel-rail pressure, is also making them quieter, so it was inevitable this was going to be synthetic.

Sound ideas
Essentially there are three different noises. The first you hear standing near the bonnet is a very unpromising diesel chug. This is real. The second you hear again from the outside when the car is driving away. This is a lot better, a growly burbly petrol-aping menace that is actually generated from a vibrating speaker within the exhaust pipe. The third is what you hear from within the car and it's gravellier noise that's no less appealing but references the diesel under the bonnet a bit better. This is synthesised and emanates from the car's interior speakers to exact match the revs. As a backdrop to pedal-down driving, it all sounds appropriate.

The future of lag-free turbodiesels?

We love that electric turbo (sorry, compressor) though. We'll first see it an SQ7 version of the new Q7 SUV that's coming next year, according to Hackenberg. It's not cheap, because that compressor also requires a 48-volt electric system to run alongside the standard 12v. Essentially it's a mild-hybrid because a small motor-generator also feeds captured energy back into a small lithium ion battery that can also run other electric gadgets. One suggested was an electric chassis control system.

The RS5 TDI won't arrive until after the new A4 is launched next year with the new longitudinal engined architecture, but when it does finally come as we expect it to, it'll be a tempting choice for those who want their weekend plaything to also fulfill dull weekday duties with MPG averaging into the thirties rather than 20 on a good day.

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AUDI RS5 TDI CONCEPT
Engine: 2,967cc V6 twin-turbo, electrically powered compressor
Transmission: 8-speed auto, four-wheel drive
Power (hp): 385@4,200rpm
Torque (lb ft): 553@1,250-2,000rpm
0-62mph: c.4.0 sec
Top speed: 174mph
Weight: Not disclosed...
MPG: N/A
CO2: N/A
Price: N/A

 

[mrtim]

The Turbo Zet is back!

[Hackney]

Oh god, sporty diesels. Depressing.

[dlockhart]

Can someone tell me when this engine redlines? if you get a high level of torque from 1,250 rpm and have it until 5 or 6,000rpm then this is an exciting diesel/ chassis combo

[Patrick Bateman]

Now I haven't driven an RS5, but by all accounts, would it not be better to get the petrol one right first?

Are the B7 RS4 and the R8 just a glitch?

[dukebox9reg]

'Audi has embraced the black pump more wholeheartedly than its German rivals'

Ignoring the Bmw 123d, 125d and new tri-turbo a bit there aren't we?

Along with the PH favourite a remapped 335/535d

[JonnyVTEC]

dlockhart said:

Can someone tell me when this engine redlines? if you get a high level of torque from 1,250 rpm and have it until 5 or 6,000rpm then this is an exciting diesel/ chassis combo

Looks like 5k

[mssond]

Surely the M50D counts as a diesel M car?
it has nearly the same BHP and been around for awhile?

[TurboHatchback]

I really don't understand the point of this. Diesels are for economy, surely nobody who spends presumably £60k+ on a performance car gives a flying fornication about whether it does 25 or 35mpg? A 2.0tdi or maybe even the 3.0tdi can make sense for very high mileage users but as interesting as the technology might be I can't see who would actually want one of these.

[dukebox9reg]

Those electric turbos are nothing new been on EBay for years..........

[WCZ]

"Electric compressor"

and to think how we all laughed at the 'electric supercharger/turbonator' :P

[Nors]

TurboHatchback said:

I really don't understand the point of this. Diesels are for economy, surely nobody who spends presumably £60k+ on a performance car gives a flying fornication about whether it does 25 or 35mpg? A 2.0tdi or maybe even the 3.0tdi can make sense for very high mileage users but as interesting as the technology might be I can't see who would actually want one.

Regardless if you're right or wrong, is £60k+ a lot for a 'diesel' these days. Huge amount of manufacturers have various diesel cars way in excess of this amount, not specifically promoted as performance vehicles either.

Personally, I like the idea of crazy neck breaking torque delivery with no lag, but that's me.

It might be a move by Audi to put a diesel Halo model out there to promote/gain some success from their Le Mans investment??

Don't like? - Don't buy, but I'll bet these will sell!!

[unpc]

Hackney said:

Oh god, sporty diesels. Depressing.

I drive a supposedly sporty diesel. It's a cracking car apart from the oil burning bit under the bonnet.

I'll pass thanks.

[vee5]

Ghastly. More weight, complexity & cost to fix a "problem" created by the marketing department.
As for the synthesised sound, that's like putting lipstick on a pig. It's a diesel , just accept it sounds crap, although I have no doubt this will appeal to the same "want it all" sector who would purchase a cross over, or maybe a fake designer watch?
Why not fit the compressor to a petrol turbo?

[Clivey]

unpc said:

I drive a supposedly sporty diesel. It's a cracking car apart from the oil burning bit under the bonnet.

I'll pass thanks.

Diesels are great for boring commutes, company cars that spend all day on the Motorway and for off road vehicles / overland travel but in anything with sporting pretensions, it has to be a petrol motor and that's not about to change.

The diesel hybrid Audis were undoubtedly the dullest cars at Le Mans this year; they even manage to take the sparkle out of winning the 24H.

One more thing:

Article said:

Weight: Not disclosed...

Ouch.

[dukebox9reg]

vee5 said:

Ghastly. More weight, complexity & cost to fix a "problem" created by the marketing department.
As for the synthesised sound, that's like putting lipstick on a pig. It's a diesel , just accept it sounds crap, although I have no doubt this will appeal to the same "want it all" sector who would purchase a cross over, or maybe a fake designer watch?
Why not fit the compressor to a petrol turbo?

Exhaust note wise the V6 diesel audi's sound alright under load with something like a Milltek fitted. Shame still sounds like a tractor unit under the bonnet.

http://www.youtube.com/watch?v=_EiWkkJZY0Y

[TobesH]

My choice of fast diesel...




Performance
Acceleration 0-100km/h (s) 4.6
Top speed (mph (kph)) 173 (278)

Fuel consumption *
Urban (mpg) 47.1
Extra-urban (mpg) 57.6
Combined (mpg) 53.3
CO² emissions (g/km) 139
Efficiency category B

[Stu R]

TurboHatchback said:

I really don't understand the point of this. Diesels are for economy

Diesels are for torque. Economy is a just a plus in some cars where there's not a lot of work asked of them or weight to pull. My pick-up barely betters what the V8 petrol can do MPG wise, but it'll pull a house down and barely know it's there.

While I'd never choose one over a nice rev happy engine in a sports car application, the RS5 is not a sports car, it's a fast GT bloater. It'll probably work pretty well with a big diesel, and in the bigger stuff like Q7s where it's nice having sufficient poke to get to cruising speed in no time at all, in one effortless and smooth surge.

It's very much a case of horses for courses IMO. For non-enthusiastic, relaxed cruising it's perfect to me.

Edited by Stu R on Tuesday 22 July 12:45

[JonnyVTEC]

Looks like it will go in the Q7 first anyway which is more palatable powerful diesel offering; thats where we saw the bonker V12 diesel.

[renaultgeek]

Why is everyone so down on this, the petrol one still exists and it still needs a driver. 2 things to be thankful for.

[sleep envy]

Stu R said:

TurboHatchback said:

I really don't understand the point of this. Diesels are for economy

Diesels are for torque. Economy is a just a plus in some of them where there's not a lot asked of them. My pick-up barely betters what the V8 petrol can do MPG wise, but it'll pull a house down and barely know it's there.

While I'd never choose one over a nice rev happy engine in a sports car application, but the RS5 is not a sports car, it's a fast GT bloater. It'll probably work pretty well with a big diesel, and in the bigger stuff like Q7s where it's nice having sufficient poke to get to cruising speed in no time at all, in one effortless, smooth surge.

It's very much a case of horses for courses IMO.

Nailed it.