Carbon buildup update

[bluenosewrx]

Dont worry terry i am confused as well, this could go on a while,lol

Mac

[SimonC]

I ought to go on confused.com. Is it a fact that all FSI engines suffer from this type of carbon build up? and no one has noticed this before because there has been no significant power loss or any other engine problem to warrant opening it up and thus seeing the build up. I am not an engineer.

This is likely to be specific to certain types of engine and will vary depending on usage, climate, oil type, fuel type, etc. Adapting an engine rather that designing it to operate that way from scratch is more likely to cause such problems. I think most people now expect well over 100000 miles from an engine without mechanical repairs. If an engine shows signs of not achieving this then I would consider that to be legitimate cause for disappointment.

If I had one of these engines, I would now be seriously considering an LPG conversion - this would have the dual benefit of cheaper fuel for driving hundreds of miles at part-throttle (ie the times when a smaller engine would suffice) and the indirect LPG injection would keep the inlet tract clean.

[almoRS]

LPG conversion on a V8?! Let's be honest. You don't drive an RS4 B7 for fuel economy.....

[Sims]

Dont worry terry i am confused as well, this could go on a while,lol

Mac

Certainly looks like. I read this somewhere else.

My personal opinion is the RS4 get it bad because it revs so high, and the breather system (thats supposed to send oily vapor back into the engine) cant cope at the high revs and is actually sending large oil droplets (one of the reasons they burn so much oil) then the EGR sticks to the oil droplets and you get sticky oily carbon on the inlet valve.

If you put a race car breather system, with a big catch tank, on the engine, I'm sure it wouldnt happen, dont know if that would be permisably for euro 4 regs though.

[SR71]

The problem is that the RS4 doesn't have EGR, at least, not in the traditional sense.

The pictures you see after 2000 miles are, as I understand, with the line from the cyclone to the manifold completely blocked off i.e., there was no way in that 2000 miles that any crankcase vapour could physcially get into the manifold.

Thus, the only postulated sources of the contamination that has built up is leakage past the valve seals and/or flow reversal effects.

Yet the runners themselves are covered in deposition as well.

In the early days, I think the suggestion was that the cyclonic seperator was failing miserably at its job and letting a huge amount of oily vapour back into the manifold, which combined with a severly lowered flash point, resulted in the phenomenon.

However, at least 2 things seem to discounted this as the predominant mechanism: 1) MRC blocked off the pathway completely and yet deposition is still occuring, and 2) Arthur's observation that in 200 miles of motoring some gauze stuffed in that line evidenced no oily residue.

FSI engines tend to run at temperatures that leave the valves at the optimum temperature for deposition, hence the problem.

To me, some of those valve stems look like they are gradually burning?

If I recall correctly, my full titanium Akrapovic exhaust on my 12R gradually change coloured over the years, and went through that colour phase before finally going blue. I'm fairly sure my exhaust headers showed similar discolouration as well... I'm not sure about the passivation properties of Titanium...anyway I think the RS4 intake valves are coated in chrome?

Like you say, the simple solution if the culprit was crankcase vapours is to plumb a line back into the exhaust headers to scavenge the flow straight into the exhaust where it'd be burned off with nil (as far as I'm concerned) consequence.

But I think its more complicated than that...

Just as a note, one of Rob's complaints when the car's PCV system was re-jigged was the odd smell of oil vapour in the cabin...

[ArthurPE]

Yes thats correct, athough the work first began at 20k miles.

I think maybe your right SR71, and the car was returned to default after the 2000 mile experiment.

so you are saying after the 2000 mile cleaning was done the breather was reconnected? put back to factory spec?

and the 6000 miles were run with the oem breather system?
becasue the 6000 deposits are mild, look at the port walls...

[svassileou]

I remember reading the "high revs" comment that sims posted somewhere on here too. Does this mean that if you don't use high revs the issue is...erm...less of an issue?

[ArthurPE]

I remember reading the "high revs" comment that sims posted somewhere on here too. Does this mean that if you don't use high revs the issue is...erm...less of an issue?

I would think high load and revs would help
low speeds/lugging usually exasperate the deposit formation...

[victor2vt]

Just had mine in for service, 32k miles, with a main dealer RS mechanic who knows his stuff, says not to worry about this issue and he

WOULD tell me if he thought it was going to be a problem.

[ArthurPE]

Just had mine in for service, 32k miles, with a main dealer RS mechanic who knows his stuff, says not to worry about this issue and he

WOULD tell me if he thought it was going to be a problem.

good to know...


regarding:
My personal opinion is the RS4 get it bad because it revs so high, and the breather system (thats supposed to send oily vapor back into the engine) cant cope at the high revs and is actually sending large oil droplets (one of the reasons they burn so much oil) then the EGR sticks to the oil droplets and you get sticky oily carbon on the inlet valve.

If you put a race car breather system, with a big catch tank, on the engine, I'm sure it wouldnt happen, dont know if that would be permisably for euro 4 regs though.

as far as the blow-by overwhelming the cyclone seperator at high rpm's, doesn't seem likely...

1 cyclones are usually MORE efficient at higher flows ~ velocities
there are 3 in parallel sequenced by a spring loaded piston valve...
very efficent over a wide range, well thought out...

2 as you can see from the posted pics in this very thread, the blow-by was vented to atm, completely removed from recirculating, and yet after 2k miles the valves had deposits...

which tells me it's the valve seals...

[Sims]

An aircraft engineer I come across mentioned the use of ground walnut shells to clean problem aircraft engines. Has anyone come across this?

To be fair it was just a casual conversation so no great details entered into - feel comfortable to blow this idea away.

[Billy]

Yes thats correct, athough the work first began at 20k miles.

I think maybe your right SR71, and the car was returned to default after the 2000 mile experiment.

so you are saying after the 2000 mile cleaning was done the breather was reconnected? put back to factory spec?

and the 6000 miles were run with the oem breather system?
becasue the 6000 deposits are mild, look at the port walls...

Yes after reading back through Rob's and SR71's post I believe it was returned to default.

So the deposits look good for 6k miles imo.

Now how this relates to power well.....


Lets say for example Audi are correct, and the deposits seen when the manifold was first removed are normal. So if you were to put this engine on a bench dyno, and everything else is working as it should, it would produce 414bhp.

Now if you the have valves cleaned and inlet manifold ported and polished it makes sense that it's going to help with airflow and increase bhp. If this process then helps stop the carbon returning to it's original levels, your going to keep plenty of the power gained from doing this surely.

What I'm trying to say is even if you think cleaning the valves and having the manifold ported and polished is unnesscesary because the engine makes it's stated bhp. Surely having the work done to increase power on top of that can't be a waste of time?

But then I suppose there's the question how much power does it actually give, I think the figure was 24bhp when Rob first had the work done.

Then there's also the question is it worth the cost.

[Terry1948]

Billy I think it is a classic case of diminishing returns if you already have N/A engine putting out a lot of hp extracting more is going to cost a lot of money for a small increase.Its the same in any high quality product and if you want to and can afford to why not.

[Sims]

Ok I was in two minds whether to start this thread as it has become a topic of much heated debate recently.

But I thought people still might be interested on how Pippyrips old car is doing since it was first cleaned a few months back.

The car was at MRC recently and while there I asked Doug to clean the valves. This wasn't because I felt the car was down on power at all, I was just curious.

Here are the pictures from when the manifold was first opened














The manifold was then cleaned, ported and poilished.


Here are the pictures from when the manifold was removed again 2000 miles later









The manifold was cleaned once again and here are the pictures 6000 miles after that


















So thats where it's at now.

To me the there doesn't seem to be any difference between the 2000 mile and 6000 mile pics.

So while not preventing it completely I think the work MRC did definitely had a postive effect on reducing the buildup over time. Maybe this is as bad as itl'll ever get, we'll see.

Whether you believe this to be significant in power debate is upto you. All I will say is while I admit I'm no engineer, seeing the pictures from when it was first opened up compared to the last ones. If someone showed them to me and asked which engine do you think is putting out more power?

I would say the last ones. But like I said I'm no engineer so I'll admit I could be 100% off the mark.

!

If the Audi team was to drive the Nurburgring 24hr race, and they had a choice of what the above three states of engine, or a super clean one, which one would they go for?

[SR71]

Hey Victor, has the mechanic in question seen the images in this thread?

Well it was worth it for you Billy because Rob paid for it! Hehehehe.



I do agree with Arthur that the valve seals must be a major culprit.

But look how far upstream the deposition extends?

The Audizine thread shows that even the manifold flaps are covered in ****.

If no vapour is coming through the cyclonic separator as Arthur has observed, then how the hell is all that stuff getting back up there?