Technical Shrick Stage 1 Low-Lift cam results

bakerdou

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@martymil FWIW I'm having the same false knock on supertech valvetrain with high lift cams. Ported N54 head.
May I ask did the false knock persist and what was the cause of your false knock?
My builder told me if I left too much of room between the piston and the bore, say, more than 0.07-0.1mm or some, false knock may occur.
I am going to use the exactly same setup with my head as yours, not sure if there is any issue I need to prepare myself for.
 

martymil

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I ended up getting the custom knock sensors from vtt and fixed all my issues.

Got the motor in my e87 now and it's flawless
 

JohnDaviz

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So.. The DME is not listening and checking the recorded frequencies? A knock sensor is not a microphone and just a slave of the controller?
If you change the bandwith of a knock sensor the DME cannot react with the tables in your map because the knock sensor would not deliver the requested data.
If frequencies are removed .. this is not a total desensitizing of a frequency?
 
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bakerdou

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I ended up getting the custom knock sensors from vtt and fixed all my issues.

Got the motor in my e87 now and it's flawless
vtt discontinued this knock sensors anyway. Finger crossed for my rebuilt motor, not yet assembled.
 

martymil

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vtt discontinued this knock sensors anyway. Finger crossed for my rebuilt motor, not yet assembled.
In my case the motor was silent and never had issues, what started the false knock for me was the cams.

Some noise the cams made that my IKMOS just didn't like, I still pickup up knock when it happens as you can see it in the logs.

Prior to the cams I never had any timing corrections at all and I would never run desensitized knock tables unless i was on straight e98.

Glad I got them when they where available.
 

fmorelli

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So.. The DME is not listening and checking the recorded frequencies? A knock sensor is not a microphone and just a slave of the controller?
If you change the bandwith of a knock sensor the DME cannot react with the tables in your map because the knock sensor would not deliver the requested data.
If frequencies are removed .. this is not a total desensitizing of a frequency?
I don't know exactly how they do it on the N54, but my understanding is that what is being listened for could be harmonics - second order and so on. That does not happen in the sensor - requires a computer algorithm to sort that out. But can certain effect the range which one would want the sensor to function.

Long ago, I understood from a engineer that was doing early Porsche development, that the reason for going after the harmonics was that the 2nd order harmonic frequency was in a far less noisy frequency band.

I don't know how one takes an existing sensor and desensitizes it without putting a filter on its output. With a filter, the only other way I would know is to literally have the sensor be a different product with a different characteristic set.
 
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JohnDaviz

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I don't know exactly how they do it on the N54, but my understanding is that what is being listened for could be harmonics - second order and so on. That does not happen in the sensor - requires a computer algorithm to sort that out. But can certain effect the range which one would want the sensor to function.

Long ago, I understood from a engineer that was doing early Porsche development, that the reason for going after the harmonics was that the 2nd order harmonic frequency was in a far less noisy frequency band.

I don't know how one takes an existing sensor and desensitizes it without putting a filter on its output. With a filter, the only other way I would know is to literally have the sensor be a different product with a different characteristic set.

The DME reads the whole vibration bandwith the piezo element within the knock sensor is calibrated to. I would assume it is not only reading a specific harmonic but rather the DME is looking for for a specific frequency. Everything has its own resonance frequency and on top of that harmonics.
So this is the core issue of the DME. Your motor mounts, dmfw, trans, sub frame.. etc..etc.. can trigger a knock as different parts can have the same frequency in different harmonics.

So our knock tables are calibrated for stock power and if you double that hell brakes loose as tons of other parts start vibrating in other frequencies than they are supposed to and can overlay with each other or.. cause false knock as the same vibration is caught as the DME thinks only can come from the combustion.

When our NVH Team analysis our compressor they are also looking for frequencies/harmonics that are suspicious. When they present the results to us it looks like this.
Bildschirmfoto 2022-04-01 um 15.10.14.png

You have the base frequency and all (or a lot) harmonics recorded. The DME gets the whole vibration transferred to the knock sensor. The piezo element in the knock sensor gets the vibration and transforms it into an electrical signal which is then forwarded to the DME. The DME takes the knock sensor tables and pulls timing when the signal triggers "knock".


If it is the first or second order i don´t know. But there is nothing like marty describes except it would be delivered with additional electronics that filter out things before forwarded to the DME.

The VTT crap is just a stock knock sensor with a different resistor. So just a desensitized sensor so that our DME doesn´t trigger as early. The same thing as back when BMS put a resistor between the sensor cable and the dme.
cgm2_p139_00_900x473.jpeg



The basis of the VTT "custom" sensor. No wonder they are not sold anymore.
attachment.jpg
 

nyt

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The VTT crap is just a stock knock sensor with a different resistor. So just a desensitized sensor so that our DME doesn´t trigger as early. The same thing as back when BMS put a resistor between the sensor cable and the dme.
View attachment 66127

The basis of the VTT "custom" sensor. No wonder they are not sold anymore.

Looks like a bit more than a resistor, but not much more. A simple filter network.
 

martymil

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The vtt sensor is totally different to the stock sensor and much bigger than the factory unit, I was thinking when I get it there would be a part number but no such luck and he is keeping that info to him self.
 

martymil

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Terry runs the vtt sensors not the original trim pot ones he had, the only thing they use from oem sensors was the plugs as you cant buy them separately and source new sensors which I know Tony cant get anymore as they have been discontinued as I wanted to buy two more sets.

If they where oem modified I would have got at least 10 sets as I get asked about them all the time as lots of people are having issues with false knock. The only way to truly avoid it is run clean e85 to e98 and turn knock control off via the tune to get rid of it, even desensitizing the ecu doesn't help sometimes but I wont do that as that's up to the individual to do themselves.
 
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Tzaks

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vtt discontinued this knock sensors anyway. Finger crossed for my rebuilt motor, not yet assembled.
Have you finished your engine build? In the process of building mine and not sure if I should pull the trigger on the camshaft especially since they went up in price 20%.

Anyone else that can advise?
 
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bakerdou

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Have you finished your engine build? In the process of building mine and not sure if I should pull the trigger on the camshaft especially since they went up in price 20%.

Anyone else that can advise?
Still in progress, will report back when it's done. Got high shirick from Maxrpm Germany eventually for my build.
Not sure about its utility tbh, I am expecting the head porting job by myself to pay off more than cam swap though.