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? |
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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Originally Posted by 18psi
(Post 436174)
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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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... |
Originally Posted by Spookyfish
(Post 436193)
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 haven't revved stationary to 5K, but even at lower RPM's I see the knock move off zero. |
Then you need detcans to be sure...
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Originally Posted by Stein
(Post 436195)
I haven't revved stationary to 5K, but even at lower RPM's I see the knock move off zero. |
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:mad: I guess I'm starting to make enough torque/power to overwhelm the poor fella:D 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. |
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. |
Originally Posted by sixshooter
(Post 436255)
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.
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. |
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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Originally Posted by ZX-Tex
(Post 436269)
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.
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. |
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 |
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. |
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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