Pictures of my inlet ports....

[SR71]

Another shot from MRC...

Its so bad I can't even see what is going on in there!

[lengster1]

Crikey and i was undecided due to current thread/debates on wether to have them cleaned as part of the tune but surely that cant be good for flow?

[ArthurPE]

a RR will never accurately measure power...period
If I tried to use a ramp test for power rating I'd be laughed out of the industry...
it needs to be steady state, applying power at power peak until it bogs down, back off, let stabilize, and record...
factor in the RS4's variable torque engine and awd system/asc/etc., it becomes even more nebulous..

a 2% increase in airflow is ~1% in power, most engines (otto cycle) convert 50 to 60% effciently...so 1+% ~ 5HP...the same as a few degrees of temperature change or a few mb of atm P...
not to mention vagcom flow measurement accuracy is at best 5%, but probably closer to 10%...2% is lost in the noise
and means even less without knowing: temp/humid/atm pressure/speed/etc....7800 rpm in 2nd is a lot different than 7800 in 3rd

P_G
I've posted Audi's test procedure, (well not Audi's, but EEC mandated procedure that is performed by a third party) I'll try to dig it up again, it's an EEC std...
full power, at multiple points, 1 minute to stabilize, 1 minute running to record an average...they also are broken in engines with carbonization, it specifically states that in the standard...

[sonny]

Well I drove the OP's (Zorbs) car last week who had the head work carried out by MRC, we compared both cars (with and with out head cleaned). the difference between the 2 was like day and night.

I have just returned from MRC after having some work carried out...differance..YES!

I have done pre and post 3k-8k runs, however I have not yet finished (As fuel levels was wrong), I will post a write up after I get back from Silverstone tomorrow, as I will be testing the car on the track and putting it through its paces.

[lugars4]

I would have to agree about your view on the airflow restriction of the carbon deposits not being likely to cause a noticeable decrease in power up to a certain point. But it would depend on how bad the carbon buildup gets.

I would be more interested / concerned with the effects of carbon deposits causing poor seating of the inlet valves, and possibly contributing to or causing a detonation problem, with the result of timing pull. Which could, without doubt, cause a noticeable power loss.

It would be worthwhile taking a VAGCOM log of the timing correction factors and comparing pre / post clean-up of the inlets....

[SR71]

Cleaning is worth 10 degrees of timing.

Observed many times.

[lugars4]

Cleaning is worth 10 degrees of timing.

Observed many times.

Well that's where the power is lost. not by physical inlet restriction.

I will be logging the timing of my RS4 (when i get one), and making a decision on pulling the inlet based on what i see, over a range of driving conditions.

[P_G]

Cleaning is worth 10 degrees of timing.

Observed many times.

And how many degrees of timing before power output is affected and by what percentage? Genuinely I'm curious. And what range is there?

[ArthurPE]

Cleaning is worth 10 degrees of timing.

Observed many times.

how can it affect timing?

it doesn't cause detonation?
it doesn't produce too much torque/traction loss?
doesn't impact throttle position or piston accel speed? ie, torque demand

timing advance only helps under certain conditions...

[lugars4]

Carbon deposits can cause pre-ignition. If the pre-ignition is enough to cause knocking then it will pull the timing back.

Detonation / pre-ignition / knocking, what ever you want to call it, can be caused by a lot of factors, but anything that can cause a hot spot in or near the combustion chamber can be a real problem. Even running a cooler grade spark plug on turbo engines is enough to allow the timing to be advanced more.

I would image that the pre-ignition is a mixture of carbon deposits entering the bore, and the flame front meeting a poorly seated valve with carbon buildup.

[ArthurPE]

then that would be recorded, it has not been...
the knock sensor will set a bit

the timing may be retarded, but it's not detonation...

Carbon deposits can cause pre-ignition. If the pre-ignition is enough to cause knocking then it will pull the timing back.

Detonation / pre-ignition / knocking, what ever you want to call it, can be caused by a lot of factors, but anything that can cause a hot spot in or near the combustion chamber can be a real problem. Even running a cooler grade spark plug on turbo engines is enough to allow the timing to be advanced more.

I would image that the pre-ignition is a mixture of carbon deposits entering the bore, and the flame front meeting a poorly seated valve with carbon buildup.

[lugars4]

then that would be recorded, it has not been...
the knock sensor will set a bit

the timing may be retarded, but it's not detonation...

Carbon deposits can cause pre-ignition. If the pre-ignition is enough to cause knocking then it will pull the timing back.

Detonation / pre-ignition / knocking, what ever you want to call it, can be caused by a lot of factors, but anything that can cause a hot spot in or near the combustion chamber can be a real problem. Even running a cooler grade spark plug on turbo engines is enough to allow the timing to be advanced more.

I would image that the pre-ignition is a mixture of carbon deposits entering the bore, and the flame front meeting a poorly seated valve with carbon buildup.

Your right! It never develops into concerning detonation, but the prescence of detonation is what the knock sensor detects, thus retarding the timing, to protect the engine from further more prominent detonation. The retarded timing is then the reason for a small loss in fuel efficiency, and ultimately, power.

[ArthurPE]

if deposits cause detonation/pre-ig, ALL cars would suffer, consider:
all cars have deposits to ~ the same degree, none a re immune...
all fuel is ~ the same quality
it will not be intermittant, and will not go away, and may get worse, it's a continuous, degrading phenomena
if timing is reset to limit, as it would be for a continuous worsening condition, a check code would be set, limp mode imposed, and the ecl would flash, ie, stop! don't drive it...

there would be 100's, ALL cars suffering from this...
the times I have indicate otherwise...it's very limited, and usually not deposits...

the only thing deposit related that may cost power is gummed up manifold flaps, not the gunk on the valves per se

[lugars4]

Some interesting and valid points !!

One of the main contributing factors to pre-ignition is carbon deposits, Fact. Albeit mostly on the hotter exhaust sides of the head.

But it has been reported on a number of occasions that timing <beep> (large correction factors) have been noted before a cleanup. Maybe coincidence..?!

Not ALL cars have this level of carbon buildup, especially on the inlet valves at such a short interval, on such a high revving tuned engine....

The carbon builds up to a "maximum" in under 10k?. What happens to the excess carbon that is produced but does not continue to build up? It must enter the bore, and no doubt some carbon buildup would be seen in areas of the bore itself.

Audi have often been asked to investigate many running problems on cars later found to have carbon buildup. They measure the timing and knock from cold and if they detect misfires their common answer is to dump fuel treatment into the tank. They drive the car for a number of miles to flush it through and the morning after they start the engine and monitor for misfires, non are seen and they give the car back to the customer feeling happy they have cured the problem.
This is to cleanup and easy any deposits / buildup in the bore. But after a short period they are bound to return! With the same diminishing results.

I just find it all interesting as it ties together.

[2manytoys]

Hey guys,

I thought I'd chime in here.

Short story for those they don't know, I took my car to Audi for what felt like low power. The car began to ping, then starting pinging bad after a few months (all the while Audi trying to find the problem). A log file was sent to Germany who said the Air Volume was lower than expected (yes I had the fuel additive too). Timing was also around 9-13 degrees. Anyway, the intake was removed and valves cleaned (short story again was they were worse than this):



They were then cleaned and the car was powerful (for a while anyway, then MAF Fault, then Intake Runner, and pinging coming back).

The manifold was then replaced. What we found when it was removed was this (notice the chuck of carbon that has fallen off, this was shiney when I first saw it, but it's dull in this picture as it was taken two days later)



The pinging I experianced (probably due to carbon, and confirmed by Audi Australia as the likely cause) made my piston look like this (you'll see in the video that the first piston is from an RS4 that has carbon but doesn't yet ping, you'll then see mine). I was going crazy at Audi to fix it, all the while saying it wouldn't cause damage - yet to be confirmed)

http://www.youtube.com/watch?v=n7I4OAQHm7c

I hope this real life experiance helps guys. Sorry no formulas and theories from me, just pictures and video, I know it's not as meaningful