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Knock Control Setup Frequency - G4x


Electredge
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7K narrow will see that.  

However, just for your interest, I rarely find the calculated frequency is ideal.   Below is a pic from me doing some testing on our EJ207.  The calculated frequency based on the 92mm bore size for the engine would be about 6.2KHz.  

Frequency is on the Y axis of this pic.  If you look at 6.2K, there is so much noise it is hard to really see any difference between knock and no knock.  If you look at the 2nd harmonic of this at about 12.4K, it is not really any better.  In fact about 8-9KHz has the best signal to noise ratio for determining knock in this case.  

But what Im getting at is the bands are usually quite wide - +/-0.5KHz is not going to make much difference.  

a2hdPPz.png

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3 hours ago, Adamw said:

7K narrow will see that.  

However, just for your interest, I rarely find the calculated frequency is ideal.   Below is a pic from me doing some testing on our EJ207.  The calculated frequency based on the 92mm bore size for the engine would be about 6.2KHz.  

Frequency is on the Y axis of this pic.  If you look at 6.2K, there is so much noise it is hard to really see any difference between knock and no knock.  If you look at the 2nd harmonic of this at about 12.4K, it is not really any better.  In fact about 8-9KHz has the best signal to noise ratio for determining knock in this case.  

But what Im getting at is the bands are usually quite wide - +/-0.5KHz is not going to make much difference.  

a2hdPPz.png

very interesting... have you done this test with any other motor? 

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Yeah I have done a few over the years when Im interested enough but dont usually keep the spectrogram.  That one above was more recent so I still had the files on my laptop.  Mostly odd engines that not many would be interested in anyhow.  But one example I do remember is my Evo 7 (86mm bore) was similar to above, they have a resonant frequency type sensor standard (centered around ~13KHz), but the best frequency for knock detection according to the spectrogram was about 7.5K.  I think calculated frequency was about 6.6KHz but ended up working nice at 8.    

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On 1/20/2022 at 9:12 PM, Adamw said:

Yeah I have done a few over the years when Im interested enough but dont usually keep the spectrogram.  That one above was more recent so I still had the files on my laptop.  Mostly odd engines that not many would be interested in anyhow.  But one example I do remember is my Evo 7 (86mm bore) was similar to above, they have a resonant frequency type sensor standard (centered around ~13KHz), but the best frequency for knock detection according to the spectrogram was about 7.5K.  I think calculated frequency was about 6.6KHz but ended up working nice at 8.    

I would be very interested in your EVO one if you find a pic of it.  I just did some tuning on an EVO 9 and wanted to dial in the knock control. 

 

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