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Old 07-29-2009, 03:30 PM   #1
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Default Knock on logs

I always have a big knock spike in my logs from 4300-5000 at WOT, but I also have a corresponding spike at 5000-4300 when decelerating from previous boosted run. That makes me think there is something funny with my knock sensor or just noise.

I've never heard a single case of knock on this car, I'm only running 7 psi, super conservative timing (17* 3500 and 4000, 18* above 4000) and 12 - 12.3 AFR's so I have a hard time believing this is knock. Can knock show up under 30 kPa deceleration?
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Old 07-29-2009, 03:33 PM   #2
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Don't know about deceleration, but I have the same knock. It usually doesn't show up in 1st or 2nd, only 3rd and 4th. Its at 0 and then at 4500ish or so it just SPIKES like mad. Like 40-50-60 counts or so. Running 8psi, about 18* timing in boost, and afr's rich as hell at low 11's.
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Old 07-29-2009, 03:38 PM   #3
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Quote:
Originally Posted by 18psi View Post
Don't know about deceleration, but I have the same knock. It usually doesn't show up in 1st or 2nd, only 3rd and 4th. Its at 0 and then at 4500ish or so it just SPIKES like mad. Like 40-50-60 counts or so. Running 8psi, about 18* timing in boost, and afr's rich as hell at low 11's.
Hell, I see 120's to 140's in the extreme spikes. Take a look at your logs and see if you have them on deceleration after a boosted run as the RPM's pass back through that range. I'll have to check the first two gears, but yeah, most evident when I'm doing 3rd and 4th gear pulls. That might be because they are the pulls that I am looking for when tuning.
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Old 07-29-2009, 04:05 PM   #4
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Just a harmonic. Dial it out if you can (KnockSenseMS).
Do you also have it when revving stationairy?

I am going to make some detcans (mic+headphone to knock sensor) one day...
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Old 07-29-2009, 04:10 PM   #5
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Quote:
Originally Posted by Spookyfish View Post
Just a harmonic. Dial it out if you can (KnockSenseMS).
Do you also have it when revving stationairy?

I am going to make some detcans (mic+headphone to knock sensor) one day...
I can dial it out through the Adaptronic. You can set minimum levels for each 500 RPM. Anything less than the level will show up as zero. The only problem that I have is if I dial out the max that I have seen (140) and normal is, say 60 or 70, if I really do get knock, it may never catch it. I haven't been concerned thus far, as I know the tune is safe, but I wanted to start dialing up the boost this weekend and finally became concerned about "real knock".

I haven't revved stationary to 5K, but even at lower RPM's I see the knock move off zero.
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Old 07-29-2009, 04:16 PM   #6
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Then you need detcans to be sure...
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Old 07-29-2009, 04:18 PM   #7
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Quote:
Originally Posted by Stein View Post

I haven't revved stationary to 5K, but even at lower RPM's I see the knock move off zero.
This is weird. I NEVER see knock at idle or lower rpms.
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Old 07-29-2009, 05:20 PM   #8
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OK, just got back from TRYING to make a log. I got about 2 good pulls in 4th where I was able to see about 40-50 counts of knock. Ok great, so I go into file, make log, start log, hit the throttle, roll into boost, and.......





































CLUTCH IS TOAST
I guess I'm starting to make enough torque/power to overwhelm the poor fella
From that point on, any pull in 3-5 results in clutch spinning all the way to redline. After a few attempts to get a clean log I gave up so as not to copletely fry the thing. I have an act 6 puck ready to go in.
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Old 07-29-2009, 05:56 PM   #9
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Knock sensors are nothing but heat resistant microphones. The signal from a knock sensor is an audio signal recording engine noise. The characteristic audio signal for knock has a specific frequency that the knock detect circuitry filters out. This pitch (some frequency between 5 kHz and 20 kHz) is dependent on bore size, average gas temp in the chamber and comb. chamber shape. The knock detect circuit is factory tuned for that. On many OEM ECU's the knock circuit is switched off above ~4000 RPM, because the knock signature signal gets buried in other engine noise.

Engine mods like boring out, different pistons, different boost and so on, can change the characteristic knock frequency with the result that the ECU will listen to the wrong frequency and will not detect knock at all with it's existing sensor. I can also pick up other engine noise as knock. This being said, it is always best to use a knock sensor designed for your particular engine because it will be most closely tuned for your engine's knock noise characteristics.

Stein, if it always puts out roughly the same amount of noise under load in the same cells and you are sure it isn't really knocking, then that value really is your baseline. Additional noise would then be correctly interpreted as knock. That is exactly how the OEMs do it.
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Old 07-29-2009, 06:03 PM   #10
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Quote:
Originally Posted by sixshooter View Post
Stein, if it always puts out roughly the same amount of noise under load in the same cells and you are sure it isn't really knocking, then that value really is your baseline. Additional noise would then be correctly interpreted as knock. That is exactly how the OEMs do it.
Thanks for the background. It helps. As to the above, I'm going to log several boosted runs to see how consistent that I can make the "knock profile" so I can set said baseline. My only concern is if I can't nail down a predictable baseline due to spikes. I'm sure I can come close, though.

That said, knock CAN'T occur under deceleration, can it? If so, my baseline just got easier and I can for sure attribute the deceleration knock readings as a minimum baseline, plus adding what I see on acceleration, within reason.
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Old 07-29-2009, 06:29 PM   #11
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I saw the same spike on mine and it was not knock, did it regardless of throttle effort or timing. I plotted log data of knock versus RPM over several pulls and got a graph with the same spike signature IIRC. I think I posted about it here somewhere? I set up my adaptronic filter based on that.
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Old 07-29-2009, 06:45 PM   #12
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Quote:
Originally Posted by ZX-Tex View Post
I saw the same spike on mine and it was not knock, did it regardless of throttle effort or timing. I plotted log data of knock versus RPM over several pulls and got a graph with the same spike signature IIRC. I think I posted about it here somewhere? I set up my adaptronic filter based on that.
Oh, yeah. Thread here. I even posted in it and didn't remember it.

https://www.miataturbo.net/forum/t34218/

I'm going to do the same and establish baseline in the same way, but yours and SV's look just like mine.
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Old 07-29-2009, 07:25 PM   #13
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Hey there guys, I have the same knock in the RPM range mentioned. Does it with no load and pig rich; so I agree that it is likely just harmonics...


Cheers,
Matt
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Old 07-29-2009, 09:49 PM   #14
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I'm regularly getting knock values in the 30-70 range between 4000-5500. I'm hesitant to tune it out, but after seeing ZX's map with a spike to 100, I'm tempted to increase mine.

Also, what're you guys running for the closed loop ignition parameters? my "knock level to retard 1 degree" is still set to 1. needless to say, when I get the knock noise, it retards to TDC.
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Old 07-29-2009, 10:09 PM   #15
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I was running 1 before today. This morning I increased it to 70. Car feels SOO much better in that area. I usually see 40-50 knock or so in that range as well.
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