BoobieTrap
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« on: December 04, 2017, 08:58:30 AM »
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Hey guys,
I've been driving my 1.8t over the weekend visiting friends and family.
I normally use 98/99 RON, but where we were, there was only the standard 95 RON available. I had no choice but to fill it up with this fuel and drive gentler. However, I have done a couple of pulls just to see the difference this fuel would make.
To my surprise, the CFs were the same if not slightly better. This got me thinking and looking.
Now I have read the extensive knock related thread on this forum, which was hugely helpful and I started to probe further.
It seems that stock 1.8t cars have knock voltages that go up to 30-35V. I understand that the Voltages do not provide the full story, and the ECU is looking for certain frequencies of a certain amplitude above reference level.
Having looked at the knock related maps, it seems that the defined "window" and reference levels corresponds well with the stock voltages; for example the stock KEMLN defines the (top?) window level at 48V above 5000 RPM.
The RKRMX1N & RKRMX2N define the reference signal as 22.5V at 5000 RPM and up to 32.50V above 6400 RPM.
However, on my highly modified 1.8T APX/BAM hybrid, I can see cylinder 3 voltage up to 58V at 7.5k RPM. The others are lower but still up to 45V. Cylinder 3 always gets the most timing pull, but when I replaced spark plugs recently, none of the plugs showed signs of detonation (CF are always less than 7-8 degrees).
My train of thought is that cylinder 3 is seeing the most knock voltage (and all other voltage are higher than "stock") as a result of the following:
- My GTX30 is top mount and due to very tight clearance, the turbo compressor outlet is no more than 5mm above the valve cover and it is right above cylinder 3
- very stiff engine mounts
- Silver Project solid adjustable top mounts
- Forged internals
- Polybushes, Poly exhaust mounts
- ECU also using rate of change of load/RPM in its' calculation, which is significantly higher for a BT/high psi build
Running lower boost pressure lowers the voltages slightly, but still up to 50V (@20-22psi). Coupled with the fact that standard fuel didn't result in any worse CFs, it leads me to believe that I should look at the window and reference level maps (usually people raise KFKEFx, but I am not sure that this is the best way in this case).
Has anyone played around with these? If I understand the ECU logic correctly based on stock voltage levels, then I should increase the KEMLN up to 55-60V and RKRMX1N/RKRMX2N to the approximate average level of the voltages.
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vwaudiguy
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« Reply #1 on: December 04, 2017, 09:41:59 AM »
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Just want to add, different stations, different times of the year, different batches of gasoline, are all going to be well....Different. Basing some/all of this on the octane rating, and what sounds like a single fill-up with a slightly lower octane fuel, you might want to do more testing before placing a lot of weight on the fuel quality/octane. I would say the forged internals (pistons) would be a larger contributor than say the other things you mentioned as far as how the knock system reacts. Cool topic.
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"If you have a chinese turbo, that you are worried is going to blow up when you floor it, then LOL."
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Lost
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« Reply #2 on: December 04, 2017, 10:50:17 AM »
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Intresting topic.
Also, KFKEFx values would not be raised, It would be lowered for less filter sensitivity.
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BoobieTrap
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« Reply #3 on: December 04, 2017, 01:10:01 PM »
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Intresting topic.
Also, KFKEFx values would not be raised, It would be lowered for less filter sensitivity.
I thought it should be lowered, however it seems that whenever this map has been referenced in the past on these forums, people have almost always said "raised". |
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Khendal
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« Reply #4 on: December 04, 2017, 03:15:29 PM »
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I thought it should be lowered, however it seems that whenever this map has been referenced in the past on these forums, people have almost always said "raised".
Indeed... i 've always seen "raised" ... if raised for you is to add value  But why are you saying to lower them ? Already the forged engine is noisier, and you have false negatives... from my little experience. |
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adam-
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« Reply #5 on: December 05, 2017, 04:18:32 AM »
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This happened with Chris' build too. Niki had to numb knock because the JE pistons were noisy.
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Lost
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« Reply #6 on: December 05, 2017, 04:34:07 AM »
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Indeed... i 've always seen "raised" ... if raised for you is to add value But why are you saying to lower them ? Already the forged engine is noisier, and you have false negatives... from my little experience. Bc KFKEF It is not raising the threshold. It is lowering the senitivity. Easy to check. Have a safe tune at max 6 CF. Alter KFKEF maps both ways and see what happens with CFs. Now - nothing of this is to recommend without using aquipment for knock detection. |
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BoobieTrap
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« Reply #7 on: April 17, 2018, 12:32:58 AM »
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After playing with this a bit further, I have found that KFKEFx do not affect knock detection all that much, even raising/lowering by 20% still produced similar results.
What did make the most difference was playing around with RKRMX1/2N.
It makes sense that running higher boost pressure (along with stiff mount and forged internals) will generate higher background noise from significantly increased cylinder pressures, hence the reference levels should be increased. I have noticed that running 30psi and a load of water meth (direct port, pre-turbo and post-intercooler nozzles), I was getting lots of timing pull regardless of how much WM was being sprayed (sometimes into negative ignition timing values).
From the logs, it looks like the ECU attempts to bring the knock voltages down to this reference level, as every time the ECU pulled timing, the knock voltages came down.
I don't have access to a dyno so all my logging is done on the road. What i have done is slowly increase the reference levels, each time analyzing the raw knock voltages for any spikes or unusual patterns. This resulted in ECU pulling less timing each time (as a result I also get reduced EGTs).
I understand this approach is dangerous as I am effectively redefining how the ECUs sees knock, and can result in blown up engine; however based on my understanding of how knock sensors work and how ECU detects knock and the amount of timing I should be able to run using WMI, I am not doing anything too crazy.
If I do blow up my engine, I will make sure to update this thread in any case.
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prj
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« Reply #8 on: April 17, 2018, 05:07:40 AM »
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I hope you are at least using headphones...
Or something more fancy like the plex kit I have.
Otherwise what you are doing is pretty silly.
I've rarely had knock detection/pull issues on modified engines. Usually it's been something simple like something loose hitting the block.
What I've done usually when calibrating knock detection on standalone is I've either filled with E85 (if the fueling supports it) or race fuel, use it to set the "OKAY" reference level, and then used normal 98 RON to verify it's working alright.
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« Last Edit: April 17, 2018, 05:09:44 AM by prj »
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BoobieTrap
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« Reply #9 on: December 10, 2018, 03:00:50 AM »
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My car has been in bits for the last few months, while I was doing a few upgrades and getting a built largeport head.
Anyway, I've invested in the Plex knock monitoring system as per your advice (with dual knock sensors).
Just looking at sensor mounting options, can you please tell me where you normally mount the additional sensors?
The manual suggests the best option would be where the factory sensors are, with the second best option being the intake manifold.
I want to run these in parallel with the factory sensors so am looking for best alternative location.
Are the Plex sensors compatible with the ME7.5 ECU? Can I just split install the Plex sensors in factory location and split the output to both ECU and Plex Module?
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