Electredge Posted January 20, 2022 Report Share Posted January 20, 2022 Just wanted to see what the suggested frequency choice would be if the engine calls for 6.6khz.... I expect I could use 13khz but just wanted to see what was recommended starting point. Thanks Jon Quote Link to comment Share on other sites More sharing options...
Adamw Posted January 20, 2022 Report Share Posted January 20, 2022 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. Electredge and remski2 2 Quote Link to comment Share on other sites More sharing options...
Electredge Posted January 21, 2022 Author Report Share Posted January 21, 2022 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. very interesting... have you done this test with any other motor? Quote Link to comment Share on other sites More sharing options...
Adamw Posted January 21, 2022 Report Share Posted January 21, 2022 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. Electredge 1 Quote Link to comment Share on other sites More sharing options...
Electredge Posted January 23, 2022 Author Report Share Posted January 23, 2022 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. Quote Link to comment Share on other sites More sharing options...
mike2016 Posted January 28, 2022 Report Share Posted January 28, 2022 what would be the most ideal setting for a SR20 with stock 86mm bore? with OEM knock sensor Quote Link to comment Share on other sites More sharing options...
Adamw Posted January 31, 2022 Report Share Posted January 31, 2022 Ive never done any frequency analysis on a SR, but I would go for 6KHz. Quote Link to comment Share on other sites More sharing options...
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