Knock Algorithm (and the Low/High Oct table delta)
Thread Starter
Joined: Feb 2007
Posts: 9,486
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From: Melbourne, Australia
Knock Algorithm (and the Low/High Oct table delta)
Hi Guys,
Recently there has been quite a lot of discussion around setting your "Low Octane Timing Map" and "High Octane Timing Map" to similar values.
I would advise AGAINST doing this, from what I can see in the code the ECU basically uses the difference between the two tables divided by 0.35 (to get it into KnockSum compatible number) as a MAXIMUM limit when calculating KnockSum.
As far as I know this is new behaviour in the EvoX, as I dont recall seeing it in CT9A ROM's.
So a lot of guys get their tuned High Octane Timing map, copy it into the Low Octane and subtract 3.
What the ECU would do is the opposite, get the difference between the two maps (being 3) and divide it by 0.35 (well multiple it by 728/256) and then use that as the maximum that KnockSum can be - ie 3 / 0.35 = 8ish.
I guess the FINAL result is that the ECU will never reduce timing BELOW the Low Octane Timing Map - Although I would have to think about it some more... So for the guys setting the Low Octane Timing map the same as the High Octane Timing Map... be careful
All this information is for when Load is are ABOVE the "Knock Load Threshold" table - ie where it matters
It's late - so tomorrow I will try and uncover some more code.
Cheers
D.
Recently there has been quite a lot of discussion around setting your "Low Octane Timing Map" and "High Octane Timing Map" to similar values.
I would advise AGAINST doing this, from what I can see in the code the ECU basically uses the difference between the two tables divided by 0.35 (to get it into KnockSum compatible number) as a MAXIMUM limit when calculating KnockSum.
As far as I know this is new behaviour in the EvoX, as I dont recall seeing it in CT9A ROM's.
So a lot of guys get their tuned High Octane Timing map, copy it into the Low Octane and subtract 3.
What the ECU would do is the opposite, get the difference between the two maps (being 3) and divide it by 0.35 (well multiple it by 728/256) and then use that as the maximum that KnockSum can be - ie 3 / 0.35 = 8ish.
I guess the FINAL result is that the ECU will never reduce timing BELOW the Low Octane Timing Map - Although I would have to think about it some more... So for the guys setting the Low Octane Timing map the same as the High Octane Timing Map... be careful
All this information is for when Load is are ABOVE the "Knock Load Threshold" table - ie where it matters
It's late - so tomorrow I will try and uncover some more code.
Cheers
D.
It will even pull timing below the lower bound ignition timing map. That is supposed to be a limit map, but it doesnt limit the timing.
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When tuning cars on the dyno I also tend to make high and low maps the same "initially", since I am looking not only for the start of knock as I slowly increase timing but also making sure I am gaining Horsepower when increasing the timing.
When I'm satisfied that increasing the timing is minimal gains not worth the risk, I tend to make the Low octane map around 3-4 lower than the higher octane map depending on how conservative they want to be and this seems to work well.
It would be nice to know if you guys can figure out exactly what happens with different combos though. If the tune is right anyways, then keeping them set the same probably won't hurt unless you get a really bad tank of gas and beat on the car.
When I'm satisfied that increasing the timing is minimal gains not worth the risk, I tend to make the Low octane map around 3-4 lower than the higher octane map depending on how conservative they want to be and this seems to work well.
It would be nice to know if you guys can figure out exactly what happens with different combos though. If the tune is right anyways, then keeping them set the same probably won't hurt unless you get a really bad tank of gas and beat on the car.
I've seen cars get 10 counts of know at WOT with both maps identical.
Also, my map has always been identical below 100 load. I get upwards of 7 knocks all the time due to clutch noise.
Also, my map has always been identical below 100 load. I get upwards of 7 knocks all the time due to clutch noise.
Evolving Member
Joined: Feb 2009
Posts: 340
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From: Australia
thats not true. If I get knock, it will still pull timing way below the low octane timing map. I have my maps set to the same btw.
It will even pull timing below the lower bound ignition timing map. That is supposed to be a limit map, but it doesnt limit the timing.
It will even pull timing below the lower bound ignition timing map. That is supposed to be a limit map, but it doesnt limit the timing.
+1. I have noticed this too.
although as Bryan pointed out earlier in another thread, Lower Bound isn't THE limit map for timing. there are others.
Well in for results on this I guess.
