Turbo v Naturally Aspirated

[DuncS3]

Hi,

I notice that a lot of people on this and other boards talk about the lack of turbos on future Audis as a bad thing

So what is the big attraction with the Turbo engines?

For me, its the Turbo kick that I like, but thats about it - I mean thats just a feeling thing, not an indication that my car is fast

Obviously they are also normally easy to chip/tune, but then again if the car is quick in the first place then thats not really an issue.

so what is it?

Dunc [img]images/graemlins/s3addict.gif[/img]

[Taipan]

That's a very good question indeed, I'd be glad to read the different opinions.
Without spoiling your thread (it seems to be mentionned in the same line of posts), I also wonder why so many want a V6 over a V8.

Eric

[PhilT]

NA = Torque and then nothing...
Turbo = Torque and then whoooooosh bhp [img]images/graemlins/spineyes.gif[/img]
V6 'vs' V8 = Weight, I suppose...

[Dave]

Difficult to answer really but I will try and explain. Having had the S6 and the RS6 I should know!!

The S6 is the NA 4.2 V8 and the RS6 is the same lump but with a turbo-charger for each bank of cylinders.

The nice thing about the V8 in the S6 is that the power delivery is linear and there is always plently of torque. I can see why a lot of drivers like this type of power, because you can judge how much power you have an when.

The power delivery in the RS6 is quite different. It is of course much quicker, but you have a small period for the turbos to kick in (lag) and then all hell brakes loose. Turbo charged engines also tend to get a little wheezy at the top end of the power band. You certainly get more of a shove in the back, but it's a bit like driving a trubo diseal in that you need to keep the power in that band.. let the revs drop to 1500rpm and you will have a small wait. Now driving purists say they don't like the way the power comes in in a turbo charged car. There is little warning of when the turbo will 'switch on & off', but you can't deneigh how much extra power it gives you.

For example, say you are on a track in the S6 and you come to a bend, drop a gear and the revs climb.. reach the apex and foot down, you know you will get linear power delivery and the car will acclerate.

In the Rs6 you do the same and the power delivery is different, slow for the bend and you loose some of the boost in the turbo. This boost takes a second or two to re-adjust so the power is more 'unrefined'

In WRC cars they have a device that keeps the boost on the turbo even when the foot is off the throttle. This is so they don't suffer turbo lag. It's what makes the cars cough and splutter on down shifts.

Hope my ranting helps
Dave

[TimJMS]

Feelou has hit it on the head. Indirect throttle response.... from low rpm with turbo engines. Only other drawback that springs to mind is you really should be more careful with a turbo engine when warming up / cooling down. Turbo lag aint the issue it used to be either.

Had the pleasure of driving a new 996 Carrera 2 facelift on tuesday. Superb soundtrack with the sport exhaust. Excellent response (just like M3 / 355) to small inputs from throttle, but I honestly can say I was disappointed. Kept waiting for real accelerative thrust in the back action at some point - ANY point, and it simply didnt deliver the goods for me.

Phil - the 4.2 V8 weighs less than the 2.7tt V6!

[Riz_RS4]

Audi use turbo-chargers...... now i wonder what would happen if they adopted Mercedes method and also started to use super chargers.... no lag.... screeeeeem [img]images/graemlins/thumbs.gif[/img]

[TimJMS]

VAG have used superchargers.

G60 and G40 spring to mind. Corrado, Golf and yes!... even in the Polo.

[Riz_RS4]

So how comes they dont use them now? Are`nt superchargers better? (sorry to divert from topic)

I`ve not driven either a V6 or V8 but soundwise i prefer the RS4 rather than the RS6! RS6 sounds grumbly while the RS4 sounds silky smooth!
S3 sounds ermmmm well its acceptable atleast [img]images/graemlins/smile.gif[/img]

[TimJMS]

Riz. This would make a good thread in its own right, and you could use a far better explanation than I can give you!

Everything has its drawbacks in this arena, and my understanding is, that superchargers, since they are crank - driven rob a fair bit of engine power initially before they develop plenty of positive pressure, and so are suited to larger displacement engines? [img]images/graemlins/confused.gif[/img]

[Riz_RS4]

Its ok, just wondered thats all.
Cheers [img]images/graemlins/smile.gif[/img]

[Crafty]

Superchargers are linear, e.g. they drive like a quick NA car - theres no kick up the arse.

IMHO superchargers belong on V8s only [img]images/graemlins/smile.gif[/img]

[runrowsam]

Firstly, Tim your RS4 is GORGEOUS. I love the 19" wheels, and am trying to talk the old man into them, but he's not keen on parting with the folding! S4 looks nice too, although I'm one of life's worryers when it comes to running in and all that sort of thing! Always scared of brand new cars!

Secondly, the V6 over V8 thing. Often it's a weight issue, but the biggest problem is fuel consumption. Basically, if you think about it, each cylinder requires a certain amount of fuel just to have even a bog standard explosion, eg at idle. So if there's 8 cylinders it's gonna need more fuel. Another issue is the operative weight of the engine. This is the weight of the crankshaft and pistons etc., all of the parts which have to move. An immense amount of energy is lost in the accelerative forces involved in starting the piston head moving in the first place, then slowing it down as it starts to push up etc. Badly written, but you get my point! So the more cylinders, the more metal has to be moved about all the time, so more weight and more base fuel consumption (the amount of fuel required purely to turn the engine over). These difference are tiny, but you think about the rpm you do in a lifetime. That's a lot of times you have to multiply that weight!

Then the turbos and superchargers thing. I personally don't like the unpredictability (if you will) of turbos. I like to put my foot down and have it there. However, with such engines as the 996tt onwards, smaller turbos are used (hence the trend for twin turbos), which are lighter and so spool up quicker, allowing more rapid throttle response. They're also generally more efficient in terms of heat, as a smaller unit can dissipate more heat more quickly purely through it's surface area. Superchargers however are belt driven, effectively straight off the crank. As has already been said, it takes a lot of energy out of the flywheel to just turn the supercharger, as it's basically a compressor, hence the "Kompressor" badge on the Merc's. But as the engine starts to speed up then this is less relevant, as the usual turbo benefits of bigger bangs sort of takes over. But that energy sap does still increase as the speed of the engine speeds up, and is the reason turbos are more efficient for their power. Superchargers are definately more at home on big V8's and things, as the basic torque of having so many explosions and such a high operating mass makes the hinderance of the supercharger a lot less of a big deal.

Bugger me what a load of waffle! Hope it helped somebody though. I am the original insomniac's friend!

Rock on
Sam [img]images/graemlins/thumbs.gif[/img]

[Dippy]

It's actually much simpler than all this. Everyone here wants as much torque (and hence power) as possible. Take a NA engine and put turbos on it, and you get more torque.

So if there was a choice between a V8 and a V6 turbo in the same car, then possibly the discussion is fair. But we got a V8 turbo in the RS6. So when the new S4 has a NA V8, we can imagine it having turbos and that's the only reason why we want them.

If Audi wrote to you all saying: We've produced an amazingly small V10 that could fit into the A4, so we can offer you either a V8 turbo or a V10 RS4, I bet most of you would reply "can we have the V10 with turbos?"

[Paul-RS]

absolutely spot on!

can't beat a bit of boost! [img]images/graemlins/burnout.gif[/img]