Another stake in the heart carbon naysayers

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ads, the manifold flap runners are continuously meausred for % opening / angle and my original faults were because it could not read between 0% and 10% i.e they were getting stuck. When Audi Roadside stuck their diagnostic tool on it and pushed the white plastic arms outside the manifold with a screwdriver you could see the % movement all the way through the rane and supposedly so can the ECU's.

Oh yes I know it can read the value at any time - the question is when it actually decides to check it.
The only reason I'm not sure is that with my car pre-de-flapped the manifold arms couldn't hold position and would slowly retract back to the closed position but no error was every logged or thrown.
However when they finally gave up and refused to move the error was thrown immediately after going above 3k rpm.
Hence I'm suspecting the logic for checking flap movement versus requested position (and throwing a code when a fault is found) only happens when a change is actually requested and isn't continuous monitored.

[rs4lee]

^^^ interesting info to add. Would have been great to see you do some performance testing with such a bad case. A friend had a similar mileage rs4...never cleaned. I mentioned it above, that he cleaned it and sorted it and it is ridiculously fast now.

How is your car now?

Car is spot on ....but i now refer to rs4's as crossers that are run in hours not miles haha

we have also repaierd another rs4 that was down on power ... just by carrying out a re-learn on the intake flap runner control using vcds

[rs4lee]

However under full throttle and considering the actuators need vacuum to keep open any vacuum leak would mean that the system was now losing vacuum faster than it could generate it. So slowly but surely the manifold flaps would start to close choking off the air supply to the cylinders. Thus circa 280ps (it's a common figure) with no fault code

ads i agree with your logic ....but the thing that got me was my car had no flaps in the manifold the 3rd time it lost power ....yet it stil lost power due to a split vac pipe that supplys the vacum to the operating diagphrams for the intake flap runners.....thats what made me think its not the actual flaps starving the cylinders of air, but the ecu monitoring the runners from the postion sensors and thinking the flaps where shut at high rpm/load and the ecu deciding to pull ignition timing ?? but as i said i dont know the stratagies of the rs4 ecu to be sure ....maybe someone with more experience could enlighten us ?

[Shoppinit]

Or maybe the vac leak cause lean mixture and the ECU to pull ignition advance.

[rs4lee]

this was the carbon build up in my RS4

[bam_bam]

Jay-sus, you turn your back on one of these threads and gets out of control like some sort of Chinese Knotweed.

Rule... whatever...

[adsgreen]

To be fair... mainly got off the subject of carbon and onto vacuum
(but granted thats just as bad)

[sakimano]

An interesting development in this thread...

the two cars in question (my still bone stock RS4 and the recently carbon cleaned RS4 from the OP) went back to the dragstrip yesterday with a local Audi group. The temperature was near freezing, the density altitude was around -800 feet most of the day...so conditions for making power were great...and that showed up in the results.

Some interesting results.

My best elapsed time - 12.83 @ 109.2
My best trap speed - 12.85 @ 109.9

Back in April, I went 12.75 @ 108.3 MPH. Traction was WAY better that day, with me cutting 1.82-1.83 sixty foot times. This time unfortunately I was more like 1.87-1.91 all day. For reference on our quattro Audis, we gain a tenth in the full quarter mile when we shave a tenth off the first 60 feet, which really measures the time you take to get through first gear. At 60 feet we're going around 35 MPH or so.

The other car, has had a few modifications. First, here's what he had back when we did the original carbon clean test:

ECS Hpipe exhaust crossover in lieu of the resonator section of the stock exhaust. This is a minor help for power, mostly it's just sound. He had this on the original before and after.
JHM intake phenolic spacers - he installed these when the manifold was out.

That was it back then. Since then he has added

KWv3 coilovers, lowering the car a good 2" (from the looks of it compared to mine)
Piggie pipes - basically he gutted the PRE-catalytic converters, up close to the end of the headers where they mate up with the downpipes.

So to recap, yesterday my best was 12.83-12.85 @ 109.2-109.9.
Yesterday HIS best was 12.47-12.53 @ 113.7-113.8

!!!

Pretty huge delta. This is important for two reasons:

1. the carbon clean + piggies + intake spacers + being a little lowered = around 0.4 seconds/4 MPH gained over a quarter mile...pretty significant
2. the RS4, in the hands of decent drivers with decent mods, is running QUITE strong compared to other platforms.


As in the previous thread, I remain unconvinced that carbon cleaning is drastic and transforms the car....but I certainly think it has an impact on top end. Break down that delta however you want, just thought I would share.

[JackS4]

I hadn't updated because I haven't had time but I had my valves cleaned by Audi Dublin the Friday before last having previously had them cleaned by MRC a few years ago. I was on a pretty hard road trip to Wales the weekend before the clean and did not feel the car was really wanting much in the power stakes as it was keeping up with or faster than what you would expect an RS to do.

Following the valve clean the difference is just gobsmacking - I don't have any pre/post dyno or timed measurements but my butt dyno would tell me I must be at least 40bhp up on wherever it was previously. My Mrs and kids thought I had a supercharger fitted on the quiet such was the difference, they where just stunned.

So having had my valves cleaned twice now there is no doubt in my head that post clean you get an animal of a car in comparison to a bunged up version.

J

[bam_bam]

Queue Arthur to start doing some maths arthur.

[sonny]

Interesting, I would say the gutted pre cats was the biggest performance enhancing mod there. What was the mileage of yours and his car out of curiosity?

[RS4pete]

As with all of these things there is always the human factor. It's impact obviously varies according to the type of test (3k-8k run it has much less impact than say a lap of the ring) however, there seems to be enough evidence kicking around now (both subjective and pretty much concrete) provided by people with far more experience/knowledge than me to convince that it IS a performance issue.

To me the car is about so much more than straight line speed, I'm not particularly worried about it. If I decided to mod then id get it cleaned but wouldn't bother to otherwise as I don't see any any evidence for the buildup harming the engine mechanically.

[sonny]

Agree, I hate Ring comparisons when comparing cars as we all know a lot of that is down to the driver.

Again im not a real fan of the 3-8k test as there are to many variables, same conditions same driver would be ideal. How many ppl check their tyre pressures prior to these runs? Thats just one variable.

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Not sure what difference a driver would make on the 3-8k run
Foot down and wait

However things such as air temperature, gradient even oil temp will have impact (how much though is the golden question).

I don't think anybody has said it has no performance impact - Its pretty obvious that some chunks of carbon on the intake valves will affect things. The key point that saks and Arthur have made is that how much of this impact is actually noticable in the real world. For example, I doubt there are many people who could notice 380 vs 414 bhp.
FWIW, that works out to be the same as having a passenger in the car (wrt power to weight).

[RIV]

Carbon =