deposit performance impact

[ArthurPE]

what do you think from this limited test data?

My scientific understanding of this is inferior to yours but I have followed the threads and understand the points being made.
I also have a respect for the engineers at Audi and find it difficult to believe that FSI in itself (i.e. without other mitigating factors) can have such a flaw so you could say I am in the Arthur camp

I do think the deposits are fuel and that there is a correlation between town bound cars and greater deposits - it's been accepted for decades that a car that has done lots of short journeys needs a period of hard driving (aka italian tune-up) to perform as its best again so I don't think it's contentious to suggest a loss of performance could occur but that this would not be specific to an FSI engine

I suppose this leaves a question as to what causes an engine to lose performance when its been town bound? do you acceot this phenomenon can occur Arthur?

I don't know, town vs highway...as I said, not enough info to draw an educated conclusion..

I do know there ARE deposits, I do not think they cost much (if any) power and the benefits outweigh the drawbacks...I do think if other systems fail the deposits can grow to abnormal levels and cause problems, this is not DI, but failure of another system...in normally functioning car, not an issue...

I do think it is better (for any car) to drive long higher speed trips than around town...better all around...so I would guess yes, not 'stretching the legs' may cause performance loss...fouled plugs/injectors, etc.

I wouldn't say your understanding is inferior, just different
you seem to have a firm understanding of the system

[neckarsulm]

It's important to remember than an RS4 wasn't designed to be a town car and if it's used in this way then I think it's performance will suffer more obviously than smaller engined mainstream cars.
After all why go to all the effort of making an engine rev to 8250 rpm if it's never going to see more than 3000 rpm on a regular basis? Surely this can't be healthy?
Also I don't recall any modern car's exhaust gases smelling so strongly of unburnt fuel when starting from cold, a friend who witnessed the cold start of my car asked me if I had two black marks on the garage wall simply due to the smell - there was no smoke! So it would seem natural that a degree of running at operating temperature would be required to burn off any remnants of this rich running
In the case of PG (correct me if I am wrong) but I bet he's a longer journeys and higher revs kind of guy and his times reflect this.

[HYFR]

In the case of PG (correct me if I am wrong) but I bet he's a longer journeys and higher revs kind of guy and his times reflect this.

yeah !! sounds like my kinda guy !

(ps. im not gay (pps. despite my cab) )

[ArthurPE]

It's important to remember than an RS4 wasn't designed to be a town car and if it's used in this way then I think it's performance will suffer more obviously than smaller engined mainstream cars.
After all why go to all the effort of making an engine rev to 8250 rpm if it's never going to see more than 3000 rpm on a regular basis? Surely this can't be healthy?
Also I don't recall any modern car's exhaust gases smelling so strongly of unburnt fuel when starting from cold, a friend who witnessed the cold start of my car asked me if I had two black marks on the garage wall!
In the case of PG (correct me if I am wrong) but I bet he's a longer journeys and higher revs kind of guy.

I love to hear the 'music'
one reason I bought it

judging from the mileage, P_G's would seem to be highway use
and he's a gearhead, so I'm sure he uses it like Audi intended, lol

for my e46 M3
when commuting 50 miles x 2 each day the engine was spotless when I adjusted the valves, no sludge, shiny like polished

when I moved closer to home, 10 miles or less, never fully warm, the sludge increased dramatically..

[P_G]

Longer journeys, usually 80+ mile commute and using the full rev range whenever I can!

[Steve_C]

In my experience, using the full rev range is more important than long/short journeys. My car had previously done 20k miles pa for 3 years sitting on a motorway at 3500 rpm, i.e. all long journeys but at a fairly constant rpm. The deposits were the worst that Doug at MRC had seen and the power was down at 358PS which was one of the lowest he had seen. Since getting the engine cleaned the power is now back to 'where it should be'.

[philipwalker]

EGR and is a fairly big factor........

[neckarsulm]

In my experience, using the full rev range is more important than long/short journeys. My car had previously done 20k miles pa for 3 years sitting on a motorway at 3500 rpm, i.e. all long journeys but at a fairly constant rpm.

Good point, some motorway driven TDIs can blocked up turbos for the same reason - forgot about that

Since getting the engine cleaned the power is now back to 'where it should be'.

did you have anything else done at the same time?

[adsgreen]

My only issue is 0-anything times are so variable that not worth the bother except for pub bragging rights.
Single gear tines would be much more comparable.

Even modern cars do improve after running in and 2k miles is way to short. Gearboxes alone take a good 5k miles to get polished.

I don't think it's EGR - I read on one forum that sombody put a white nylon filter in the pipe ran it for a while and checked it and was almost perfect. This is the reason I believe a catch can doesn't help as the EGR seems to be doing it's job. It'd be interesting to see what the valve timing is doing for the different rpm - the VW patent app for the FSI seems to suggest that the carbon breaks up under heat which would indicate an itablian tune up isn't a placebo.

The only other thing I've looked at is the oil in my car generally sits around 88c when driving normally but it doesn't take alot of spirited driving to crank this up above 100c. I wonder if at the lower temp the oil isn't clearing or can't get rid of any trapped moisture. One option would be to change the oil cooler thermostat and run it a little hotter? For reference my old VXR8 using caveman technology used to sit at 110 and had similar grade oil

[Steve_C]

Since getting the engine cleaned the power is now back to 'where it should be'.

did you have anything else done at the same time?

Yes, subsequently had remap, filter etc which lifted power to 434PS. Details noted here: http://www.rs246.com/index.php?name=PNp ... 2&start=45

[P_G]

In my experience, using the full rev range is more important than long/short journeys. My car had previously done 20k miles pa for 3 years sitting on a motorway at 3500 rpm, i.e. all long journeys but at a fairly constant rpm. The deposits were the worst that Doug at MRC had seen and the power was down at 358PS which was one of the lowest he had seen. Since getting the engine cleaned the power is now back to 'where it should be'.

I believe it is a combination of factors. Long journeys are good for the cars, higher volume of air through the engine but using the full rev range as well. The one part of what you said though Steve which is always subjective is dyno readings. Yours was down at 358ps; now I haven't been to MRC and I'm not knocking what they do; that said the dyno debate has been done to death and safe to say one dyno's results should not be gospel.

Like adsgreen said one gear acceleration times and air flow readings are a far better and uncompromised set of figures than dyno readings. 358ps on one dyno could be 400ps on another with both operators suggesting theur methods and equipment are accurate.

[Steve_C]

I believe it is a combination of factors. Long journeys are good for the cars, higher volume of air through the engine but using the full rev range as well. The one part of what you said though Steve which is always subjective is dyno readings. Yours was down at 358ps; now I haven't been to MRC and I'm not knocking what they do; that said the dyno debate has been done to death and safe to say one dyno's results should not be gospel.

Like adsgreen said one gear acceleration times and air flow readings are a far better and uncompromised set of figures than dyno readings. 358ps on one dyno could be 400ps on another with both operators suggesting theur methods and equipment are accurate.

I hear what you are saying, P_G, but I look at it in relative terms rather than absolutes. My carbon was the one of the worst seen at MRC and my power one of the lowest seen. Whether the power was 358 or 400 doesn't actually matter (I agree this is subjective) - its the power compared to the average RS4 power and I would say MRC have seen enough RS4s to have a representative sample.

[adsgreen]

Dyno's are funny things - it's amazing how small variances can cause big differences. Just try one a couple times with difference tyre pressures.
Although I'd agree that MRC's rep would suggest they know what they are doing

My view on the carbon issue is that in most cases the small amounts should be unnoticable but in some instances it will cause a problem sometimes quite severe. But in all cases I think everybody would prefer it not to be there at all.

It's an interesting question though as it doesn't look like it's EGR connected as a catch tank would fix it, it doesn't look like it's valve timing issues as forced induction would fix that (and plent of Audi 2l turbo's have it as do the current generation of turbo'd mini cooper s's). It seems to get a fair way in and about the intake manifold (have seen the pics of the tumble flaps well and truely covered) so isn't likely to be blow by gases.

Has anybody seen any results as to chemical make up of the residue? is it oil based or carbon from combustion (or mixture of both?)

[HYFR]

My S3 hit 263PS on MRC dyno with 4k on the clock ... So unless they deliberately engineered that number, their dyno is pretty accurate

[adsgreen]

Problem is with dyno's is the margin of error is pretty high (relatively speaking). They are calibrated for a given altitude, pressure temp etc and it's not uncommon to have production dynamometers being acceptable with 105 margin of error. You can never read absolute figures from them and take them as given but ran as a before/after they can show a relative change.