Valves- carboning up

[ArthurPE]

it seems cars with higher mileage and no history of cleaning make rated power on the dyno

diesels have used DI forever, and their performance does not suffer
and they have much higher blow-by rates, ie, more deposits

RS4's recirc exhaust gas from one cylinder to the intake plenum and back into a different cyclinder, this will help clean the valves and seats
the seats will never foul, they are seated when the oil deposits and have the highest scouring velocity, see below...

I have shown mathematically that the restruction due to any buildup is < than that of the annualus formed by the valave and its seat
in other words, it is not the limiting factor

[BlingBling]

Fair enough however as was said in another recent thread, we are talking about a handful of cars compared to the 3000 sent to the UK and as yet none bar that handful have generated issue to the ooijt that they needed cleaning. So it is fairer to say that there could be an issue but as yet is undefined and very much a consequence on how these cars are driven.

How do you come to that conclusion? Do you have an insight into official numbers on this topic? Most of the 3000 owners are probably not car enthusiasts who do not frequent forums like these. They probably do not even know that they have a problem.

I am not and have never advocated there is not an issue, merely suggested at this point there is too much conjecture and not enough hard facts. I too will probably have the inlet manifold taken off and cleaned if necessary next year

Why would you do that?

I'm not going to lose sleep over it and would suggests potential owners do the same

The same was said about DRC a couple of years ago and yet today Audi have given an extended warranty. Would you still be sleeping well if they had adopted a similar attitude otwards the problem?

[don]

i....diesels have used DI forever, and their performance does not suffer and they have much higher blow-by rates, ie, more deposits...

I was thinking about this as well but presume it must be due to the higher combustion temperature and compression ratio in the diesel engine compared with the petrol variant. Higher combustion temperature and compression ratio must help with the decomposition of the deposits.

I presume this is why a good thrashing of the FSI engines will help due to higher temperatures and complete combustion and why short drives and frequent cold starts do not due to the richness of the mixture and incomplete burn.

[aidanjaye]

i....diesels have used DI forever, and their performance does not suffer and they have much higher blow-by rates, ie, more deposits...

I was thinking about this as well but presume it must be due to the higher combustion temperature and compression ratio in the diesel engine compared with the petrol variant. Higher combustion temperature and compression ratio must help with the decomposition of the deposits.

I presume this is why a good thrashing of the FSI engines will help due to higher temperatures and complete combustion and why short drives and frequent cold starts do not due to the richness of the mixture and incomplete burn.

So its offical - you must thrash your cars everywhere. Yippee. Gives me an excuse to tell the wife why every drive is at warp factor ten.

[SR71]

The cars that make the best power are those with cleaned, and ported and polished manifolds.

I can tell you that my Audi A3 2.0 TDi does clog itself up although its a function of the EGR system.

The symptoms manifest themselves gradually, but in my case, as a very slightly lumpy idle.

The amount of s**t in and around the EGR valve was horrendous.

I'd blank the bloody thing off if I could find someone in the UK who made a blanking plate...

I understand Audi of America has a gag order out on all their tech reps regards the matter...curious...

[ArthurPE]

How do you come to that conclusion? Do you have an insight into official numbers on this topic? Most of the 3000 owners are probably not car enthusiasts who do not frequent forums like these. They probably do not even know that they have a problem.

Why would you do that?

The same was said about DRC a couple of years ago and yet today Audi have given an extended warranty. Would you still be sleeping well if they had adopted a similar attitude otwards the problem?

the fact that so few have the 'problem' (or think they do) shows that it is statitically insignificant, ie, there is no 'problem'...
a car with 'the problem' is as fast as the car without 'the problem'
it's an imaginary issue so people prone to worry, hand wring and teeth nash away...


he said 'if necessary'

only a dimwit would 'lose sleep' over an inanimate object...
there is no DRC warranty in the US and I sleep like a baby...
if it breaks, I'll fix it, no bigee...bling bling, lol

IT'S A CAR!

[ArthurPE]

The cars that make the best power are those with cleaned, and ported and polished manifolds.

I can tell you that my Audi A3 2.0 TDi does clog itself up although its a function of the EGR system.

The symptoms manifest themselves gradually, but in my case, as a very slightly lumpy idle.

The amount of s**t in and around the EGR valve was horrendous.

I'd blank the bloody thing off if I could find someone in the UK who made a blanking plate...

I understand Audi of America has a gag order out on all their tech reps regards the matter...curious...

one of my best friends is an Audi tech at a larger dealer...there is no gag order...this is America...he does work for me on the side, and others

he said the deposits are higher in a DI engine but does not effect performance...the car makes full power at less than 100% throttle, so if there is any decrease in Q, just crack the throttle a bit more, problem solved...they have disabled the ignitions/fuel systems and run flow tests by cranking the engines and spinning them on a motor driven dyno...no difference between one with or without deposits...

the DRC on the other hand is an issue, they fail, and there will be a replacement offer later in the cars life cycle once they determine a failure rate...right now they have not seen as many as the RS6's

[ArthurPE]

i....diesels have used DI forever, and their performance does not suffer and they have much higher blow-by rates, ie, more deposits...

I was thinking about this as well but presume it must be due to the higher combustion temperature and compression ratio in the diesel engine compared with the petrol variant. Higher combustion temperature and compression ratio must help with the decomposition of the deposits.

I presume this is why a good thrashing of the FSI engines will help due to higher temperatures and complete combustion and why short drives and frequent cold starts do not due to the richness of the mixture and incomplete burn.

although combustion temps are higher due to the Cr, the operating temps are not much higher...

the deposits do not impede flow, the restriction is the valve port
the velocities are so low pressure drop is small, so all that happens is that you must open the throttle a bit more for the same power..

in the overall pressure drop equation the deposits are minimal compared to:
filter
throttle(s)
intake plenum/ports
valve seat/opening
exhaust components

deposits occur in all vehicles, but they are offset here by a high Cr, due to DI...

we can dwell on the 'problems' or enjoy the total package, 'flaws' and all...

[ArthurPE]

BMW did an intense study on this in the 80's, millions of miles...
they determined 0.25 gram/valve in 10k miles is not an issue, no loss of power or effciency...
you will see some injector cleaners boast they conform to the BMW318 standard, which is what the test was called, because they used 318i's, lol

let's put this in perspective:
1 oz (fluid) of oil weighs ~25 grams...
so ~1/100th of an oz (fluid) is cooked on the valve...0.01 oz

one of the main problems with deposits is that they absorb fuel causing driveability issues, lean mixture, then released off throttle, run on...
this does not effect DI engines, no fuel on the valves...an ADVANTAGE over port injection...

now: who's going to clean their valves perfectly:
disassemble athe head and weigh the valves
reassemble
run the engine 10k miles
disassembly, dry and weigh the valves
see if the average is > 1/4 gram per valve...

[don]

...he said the deposits are higher in a DI engine but does not effect performance...the car makes full power at less than 100% throttle, so if there is any decrease in Q, just crack the throttle a bit more, problem solved...

It is not about how much throttle but how much air flow that determines performance/output. Unless you have forced induction, obstructions in the intake are going to affect air flow, but this will probably be minimal and hardly noticeable except in the most severe cases and only really at very high RPM.

The main concern is if the issue of values not seating properly arises leading to lower compression and probably more gunk on the valves. Though I would think would take a long while for carbon to build up to that extent.

[ArthurPE]

...he said the deposits are higher in a DI engine but does not effect performance...the car makes full power at less than 100% throttle, so if there is any decrease in Q, just crack the throttle a bit more, problem solved...

It is not about how much throttle but how much air flow that determines performance/output. Unless you have forced induction, obstructions in the intake are going to affect air flow, but this will probably be minimal and hardly noticeable except in the most severe cases and only really at very high RPM.

The main concern is if the issue of values not seating properly arises leading to lower compression and probably more gunk on the valves. Though I would think would take a long while for carbon to build up to that extent.

it's actually displacement and pressure ~Cr:
M = V P/4Pi
M = moment or torque
P = mean effective pressure ~ Cr
4 = 4, Pi =3.14159...
so if the volume of the engine doesn't change, and P is ~ constant, torque does not change...

P = M w
w = 2 Pi n
n = rpm
in HP and lb-ft
M = 5252/rpm P

5252 = 60 sec/min x 550 lb-ft/sec / 2Pi

you have all the air you need at 90% throttle, it's the designed peak power point...they do this so if the filter loads up, air density, altitude (to a degree) change, you can still make peak power...Q = mass air flow

the valave seats aren't affected, this would be easily determined by a compression leak down test..

[P_G]

Fair enough however as was said in another recent thread, we are talking about a handful of cars compared to the 3000 sent to the UK and as yet none bar that handful have generated issue to the ooijt that they needed cleaning. So it is fairer to say that there could be an issue but as yet is undefined and very much a consequence on how these cars are driven.

How do you come to that conclusion? Do you have an insight into official numbers on this topic? Most of the 3000 owners are probably not car enthusiasts who do not frequent forums like these. They probably do not even know that they have a problem.

But they would be taking them to dealers complaining of issues if they felt there was something wrong with them? Plus it is reasonable to say there is arounf 5% of the UK RS4 owners on here going by the number of people who have reported against DRC. Now how many of thsoe have had issues with their cars attributable to carbonisation? It gives a number but it may not be representative plus from asking my local dealers who see a goo 30+ RS4's none have had to be cleaned because of excessive carbonisation.

I am not and have never advocated there is not an issue, merely suggested at this point there is too much conjecture and not enough hard facts. I too will probably have the inlet manifold taken off and cleaned if necessary next year

Why would you do that?

If for nothing more than to see for myself you good bad or indifferent my engine is compared to others who have posted pictures. I strongly suspect the the carbonisation on my valves is to the same extent as those who have posted pictures and little more.

I'm not going to lose sleep over it and would suggests potential owners do the same

The same was said about DRC a couple of years ago and yet today Audi have given an extended warranty. Would you still be sleeping well if they had adopted a similar attitude towards the problem?

But DRC was significant demonstrable problem, i.e. you could see and feel the suspension was not working correctly. With carbonisation you are talking about an often perceived lack of power you cannot demonstrate without taking the engine out and putting on a bench because the whole r/r not being accurate debate has been done to death and symptoms that could be a number of other factors other than carbonisation

Like said there may be an issue but until the facts are in stop scaremongering because all you do by this is put people off the cars primarily based on circumstantial evidence and may even unnecessarily devalue our cars.

[karl]

Just to add my thoughts to this; one of my valves was failing to fully seat owing to the carbon build up and this was clearly affecting performance.

[P_G]

Fair enough karl and sorry to hear that.

[reevesroadster]

I can tell you that my Audi A3 2.0 TDi does clog itself up although its a function of the EGR system.

The amount of s**t in and around the EGR valve was horrendous.

I'd blank the bloody thing off if I could find someone in the UK who made a blanking plate....

I have 2 other VW vehicles - one is a 2001 VW Caravelle 2.5TDI and I have recently blanked off the EGR. The EGR itself was badly clogged with debris and the manifold was visibly clogged too. Its done over 200K miles, and isnt an FSI engine, but the difference with the EGR blocked is amazing. More power, better fuel economy.
Im now considering the same on our 09 Touran which also has the DPF.

To blank the EGR on the caravelle it was simply a case of making a blank from some sheet steel, using the EGR pipe connector as the template.

Not sure though how this would affect emissions and the cat on our engines though, so havent done it to date.