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Is this sound detonation(knock)? Video included.
2 Attachment(s)
Here's a youtube video of what I found and believe is knock on a Renisis. I used the stock knock sensor to get the audio, please tell me what you think:
Also attached are the spectrograph pictures that helped me track down the frequency. |
its been 50 minutes and No responses yet!!
jk guys--but this is pretty exciting. |
I can't hear a knock and was always under the impression that its near impossible to get knock, more acurately described as pre detonation, on a rotary engine.
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It doesn't sound like it to me. I have heard it before in my Turbo Civic and it sounds like a "ping". Like a ball peen hammer on a plate of steel.
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Combustion chamber shape and size is much different than piston engines. Pistons ping at around 6k, 13B (REW?) is 3.5k
knock frequency on the rotary engine? - RX7Club.com It's not unreasonable to think that our frequency is different. Actualy I can hear the chriping sound from 2400-4100hz. Found this thread too, although there are no videos with working links to tell me what noise they were talking about: https://www.rx8club.com/tech-garage-...squeak-110077/
Originally Posted by MazdaManiac
(Post 1751773)
The "chirp" that is clearly recorded in the audio samples above is caused by a kind of detonation that occurs as the timing advance changes during the low RPM of start-up.
Often, you can hear this sound when you take off in first from an idle as well as the same thing is happening. It is caused by the ignition timing and it is "normal". The reason some people hear it and some don't is because of a number of factors (attentiveness being one of them), including the fact that, since this is a kind of detonation, some engines will be more sensitive to it than others. It is not damaging because the load on the motor at that moment is extremely low. The new flash may have increased the occurance of this by significantly changing the ignition timing. This may also lead to hard starts. One of the most important factors in idle emissions is ignition timing. Mazda may have been trying to offset the increased emissions of increased oil injection by advancing the idle timing. |
My understanding is the "chirp" is the timing transition change since the trailing plugs fire first during the idle phase. The chirp is caused when the timing transitions back to normal timing.
I have no way to verify this with hard evidence but due to the changing timing characteristics it made sense. This is the first time I've heard of anyone pulling actual sound from the knock sensor so it is very interesting to hear what it hears. |
i had to listen very carefully and with earphones and my volume turned all the way up to hear it--but i did. Everyones computer set up may be different of course.
Flash--doesnt that trailing transition only happen during starting? After the engine starts and is idling are the trailings still firing first? This has the possibility of being a game changer...... |
Couldn't find my spare knock sensor, so I spent the morning trying to trick the ecu. All you need is a 200k ohm resistor and the ECU has no clue the knock sensor is disconnected. Drove around a little bit and listened to the engine under load, still hearing some of the chirps. I'll change some things and try and get some solid back to back runs. Maybe run one tank of premium and one of regular. More to come as I find it.
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be careful--dont mess your engine up. Knock can be elusive.
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So not to thread jack but I have a question about this whole statement,
""The "chirp" that is clearly recorded in the audio samples above is caused by a kind of detonation that occurs as the timing advance changes during the low RPM of start-up. Often, you can hear this sound when you take off in first from an idle as well as the same thing is happening."" When I start my car first thing in the morning or if it has been off for a while, I hear a sound that sounds like a squeak or a loose belt, but it is only for a fraction of a second and does not occur again. Would this be knocking // pinging? Anything I should do about this? |
Yes it is knocking. It's very low load and not harmful, so don't worry about it.
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New video:
More analzing rotary engine knock. - YouTube I'm starting to believe in the stock knock sensor. More testing to come. |
Harlan--that sounds like knock. I am as sure as I can be.
I have actually heard this before. Of course it was much louder but the tone etc was the same. I heard it when an engine blew back in 2006. I do remember this! Man you have DONE IT! More surprises to come........I am sure. Congrats! |
Restoring the knock sensor, changing to a milder (then stock) tune and swearing off cheap gas as of now.
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If you couldn't hear it yourself - it probably wasn't knock .......................
Or should I say - wasn't the kind of knock you should give a tinkers damn about . |
Originally Posted by Brettus
(Post 4434348)
If you couldn't hear it yourself - it probably wasn't knock .......................
Or should I say - wasn't the kind of knock you should give a tinkers damn about . |
Originally Posted by Harlan
(Post 4434351)
And we wonder why people keep popping engines. :eyetwitch
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Ok, I get where you are coming from now. The whole point of this is to find knock safely(ish) at low load to pin down the frequency. I was trying to cause knock, now that I have it pinned down I can test the ecu and build on that knowledge. I haven't killed my engine yet, but that's no reason for me to chance it too much, at least not unintentionally!
BTW Brettus I'm very interested in mazdaedit, specifically if the knock tables are pinned down yet. They may become very important. |
Originally Posted by Harlan
(Post 4434355)
Ok, I get where you are coming from now. The whole point of this is to find knock safely(ish) at low load to pin down the frequency. I was trying to cause knock, now that I have it pinned down I can test the ecu and build on that knowledge. I haven't killed my engine yet, but that's no reason for me to chance it too much, at least not unintentionally!
BTW Brettus I'm very interested in mazdaedit, specifically if the knock tables are pinned down yet. They may become very important. |
Originally Posted by Harlan
(Post 4434285)
New video:
More analzing rotary engine knock. - YouTube I'm starting to believe in the stock knock sensor. More testing to come. Wow ... just wow I've heard that noise when I was NA on the stock tune. Unfortunately I've heard it while under the juice as well ... not under boost yet but under the juice. Still running same engine. |
Hey Brett--Harlan is actually trying to make sense out of the knock tables, what they do specifically , when/under what conditions and then possible progressing toward developing an ion sensing system for us.
That sure would be sweet! If Mazdaedit could have this type of ability it would be lightyears ahead of the Cobb system. |
Originally Posted by Harlan
(Post 4434351)
And we wonder why people keep popping engines. :eyetwitch
Stuff like failing to see a whole folder full of knock tables in the Cobb ATR software and such ... If you want to hear knock just set the dwell over 6mS at 4000+ rpm with GM truck coils |
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the system is rather simplistic at best, Mazda only seemed concerned in lower rpms lower temp ranges, higher load, and higher gears which makes sense on several levels
fwiw, they did add a second sensor (one per rotor housing) on the S2 https://www.rx8club.com/attachment.p...1&d=1362238703 |
While I'll agree the tables are rather simplistic, our 32bit ecu by default has a very complicated knock strategy. We use the same ecu some Subarus use and a lot of the base code comes from the manufacturer and not Mazda. Here is a link explaining Subaru knock control: Scoobypedia | Trusted knowledge for everything Subaru | Knowledge / Subaru's Knock Control Strategy Explained
Originally Posted by oltmann
(Post 4169173)
There is a knock learning strategy in the ecu and it looks just like what is implemented in every other Denso DBW ECU, right down to the values of certain parameters.
I'm not good enough with disassembly to understand exactly what, if anything, it is doing. However it doesn't seem like Cobb understood it well when they stopped working on the RX8, or for that matter even today on the Mazdaspeed cars. So, there could be a knock learning table in ram affecting timing advance, and it wouldn't show up under the knock retard pid.
Originally Posted by oltmann
(Post 4176283)
I'm saying:
- We can't log rough or fine knock learning corrections. - Turns out, we can't actually log knock retard either. - The assertion that the knock sensor cannot hear detonation is ludicrous.
Originally Posted by oltmann
(Post 4176297)
Yes, there are three ways that knock can retard spark. We can't log any of them.
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Can you relate any of those knocks you hear to a log?
Maybe track your load when you are hearing them, then lower you min load table low enough that it will corrospond with what you're hearing. I'm not scared to try it, but I'm at work. Team, With Dwell at 6MS, How bad was the knock? Did it happen at idle, or only at higher loads? |
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