toddk911

Ok got it.

What is "acceptable" knock?

I did some test runs even at lower boost and non wot and still got some counts.

1-3rd at about 18 psi I saw range of 2-4 counts.

3-4th at even under 18psi and only 5k I was getting 3-6 counts.

3-4th at 18 psi and over 5k a few times was 5-9 counts.

Fluidplay

Those are about what I was getting under WOT, running at temp on 91 oct at 18 psi
2nd -3rd 2 to 3, sometimes a 4th would pop up
3rd - 4th 3 to 4
4th - to redline would produce 4 to 6, sometimes 8

Those numbers are cut in half on 100 oct and sometimes wouldn't get any knock count between 2nd and 4th

toddk911

So even with 100 octane still some knock? That seems crazy. Lol.

So I assume some knock is expected?

jasonlp

not if your timings bang on for your octane level

Rogue_Ant

Todd - are you getting the counts during shift? That is where I get most of my counts. BTW, pulling through a gear I typically get 0-1 counts of knock.

And even if your not getting knock, it does not mean your timing is correct. One could definitely have too little, or even too much timing without knocking.

elargentino

What kind of advance are you running at around 4500 with that K27?

Mark944na86

I wouldn't be assuming every sensor event corresponds to a real knock event. In an application like this, the engineers would be using an estimate of expected "false positive" triggers to set a threshold before the DME takes the signalling seriously enough to retard timing. Disassembly of the DME code might provide a clue. But in any case, unless you notice your timing is actually being retarded by the DME, I would treat the low counts as signal noise.

The design rule in applications like these is put the intelligence and sophistication into the signal processing, rather than the sensor. Dumb sensors + smart coding is cheaper than smart sensors + dumb coding.

Rogue_Ant

That depends on boost pressure and throttle position...

The knock counter is hooked up post-signal processing... The KLR does all the signal process/conditioning looking for knock. Then outputs a knocking yes/no signal on pin 15. The only "false positives" I would ignore are those during shift, when the timing jumps erratically as the DME transitions between maps. Fortunately during shift, there is very little load - so these knock events are not detrimental.

Thom

Here is a log done today, (4th gear) - Knock counts logged on "User1".
Comments?

Rogue_Ant

I doubt the Zeitronix is fast enough to capture each event...
But it looks like your getting quite a bit of knock - what mods?

Scott H

I was wondering about logging the pin 15 output with a datalogger. If one used, say, an Innovate AuxBox, what freq. would be used to capture individual knocks?

Seems like a better solution than just event counter, this way you know at what load/RPM the knock occurred and could try tuning just that/those cells.

Another random question, when it detects knock I believe it will cut 3* of timing, then another of 3* if it continues. My question is how long is this ignition retard held? Does it keep sampling for knock to re-advance the timing or does it keep the timing cut until the load is reduced to a certain level?

Rogue_Ant

From what I've seen, you would want something in the neighborhood of 1000 samples / sec - to ensure you catch every knock event.

Good questions on the KLR, and I'm not sure how long ignition retard is held or its method for returning timing advance back to normal...
The KLR is something I plan on diving into soon though

Thom

The Zeitronix reads the signal from the SciVision KnockView which gets it from pin 15. Vitesse V-flex, etc.
I wonder if this is actual knock or just parasitic noise, since I can't feel anything particular from the seat and cannot hear knock.

Rogue_Ant

Not sure what the KnockView is...? But a spike on pin 15 is post-processed from the KLR and should be considered a knock event (unless the knock is during shift, as I mentioned earlier).

Fluidplay

This is good to know...most of my counts have always been on shift, very few have ever poped up at peak WOT. I would get 1 maybe 2 in 3rd & 4th, then get a couple more at shift. I feel much better about the tune set-up.