Now take it one step further.. if the high octane map is walking upright, and low octane map is crawling on your belly.. If you struck your head, you only would need to duck enough to clear it.. You learn over a short period of time to duck a bit to clear it.. Thats the octane number.. Its rare if you bump your head you'd drop to your stomach and crawl right? But if the danger is great enough, you might.. This is what the ECU does..

Imagine if you couldn't do that?? And your forced to stand upright no matter what.. THere's only so many times you can crack your skull before you knock yourself silly..



Ultimately the high and low maps, and the octane number, are a proactive protection from experiencing more knock for sustained period of time..

If you rely on knock sum only to pull timing when knock is experienced this is reactive, well, KNOCK IS EXPERIENCED, and a big enough incident of knock can do damage before the ECU can react to it..

 

ok, i get all that. Are you saying that the difference between having the maps the same and having the maps different is that if they are the same your timing will go back to set timing after knock is over immediatley. And if they are different it will take a little bit of time to go back to your high map?

same map = immediate response to knock, every certain period of time as soon as knock is over your timing goes back instantly to what its set to?

Different map = response to knock but, timing stays down for a period of time before coming back up?

is the octane number a timer or does it just show you where you are between the two maps? like 0-100? 100 being 100% your high map, 95 being 95% toward your high map? and 0 is 100% your low map? Is that how it is or am i wrong? Cause it seems that is what somebody was trying to say earlier?

 

For the most part yes.. However in a properly tuned car, you'd rarely leave the high octane map unless there was bad gas or some condition out of your control. Its something I wouldn't want to give up just to know that the timing will always return.. In reality a small amount of knock will always very quickly go back to normal..

I get the impression by your answer that you are seeing the flat maps as something you might consider desirable because the timing will return to normal after the knock subsides.. but on a properly tuned car you won't leave your high octane map anyway.

 

[QUOTE=I get the impression by your answer that you are seeing the flat maps as something you might consider desirable because the timing will return to normal after the knock subsides=QUOTE]


Actually no im planing on self tuning it on a road, and the safety net of switching over to the lower map is awesome. Because when your doing your pull your not sitting there stairing at your knock counts half way through the power band. So if you over advanced timing or so it would protect your motor.

In theory if you dont advance too much at a time or lean out the AFR too much at a time. As long as you keep your low map stock its impossible to melt some pistons blow your motor or whatever.
Its as if the designers et the ECU up so the everyday average Joe can theoreticly safely tune his car with a lap top and wideband.

 

^^^^^I also had planned to tune only the high octane maps and keep the low stock for maximal safety. As malibujack says, if you do it right you should stay in the high map anyway. So, tune for 0 knock. Aslo I will be tuning on 94 octane (mix of 91/100). So If for some reason I have to use strait 91, I can turn the boost down a bit but still have a nice safety margin. Then at the track use strait 100 for extra safety, maybe even turn the boost up a bit depending what the logs reveal.

Unless:
Here is the thing. With the utec, I have 5 maps to choose from.
With ECUflash although you cant switch maps with the push of a button, you can flash say a 100 octane map for race day, and the 94oct map back in for daily driving. But I'm reading that the ecu has a limit to how much its flashed. How much is this. If I plan to keep the car for say 3 years. And want to fash at max say once a week. Should I even worry? Thats less than 150 times for the word problem impaired) I would prefer to have more than 1 map to choose from.


Lastly, has anyone figured out the formula (X? counts of knock pulls Y? degrees of timing)?

PS Malibujack, that head bumping analogy was the best I've ever heard
Peace

 

MalibuJack

My head hurts!!

What exactly causes the car to run on the low octane map? How long will it run on the low map after the cause is corrected? What will make it change back to the high octane map? And no my maps are not the same.

 

Knock that occurs for a duration of time, or large knock sums that decay slowly.. The key to the Octane number is that it will move away from the problem by "ducking" until its safe to stand up again.

The formula? Well thats been discussed in other threads, I don't remember offhand, but generally counts under 5 don't shift the octane number unless it happens for a period of time, anything higher shifts the Octane number, and anything below three won't do anything, zero knock will have the octane number return over time, and how long it takes to return depends on how far away you were from 255 (or 100% in Evoscan)

Anything that will trigger the the ECU to retard timing and add fuel (knock sums) will alter the Octane number, and when the knock stops, it will stay there and slowly return, if there's an onset of knock again, it will remain at that level or go back a little, and if it subsides completely it will return.

Basically it allows a car that experiences alot of knock to compensate for these issues, without getting sudden LARGE counts of knock unexpectedly, since these things are predicated by lower amounts of knock for sustained periods of time.. Without that protection your always reacting to knock suddenly instead of progressively, which means it can do more damage by suddenly correcting (since there's the distinct possibility you will exceed the threshold for damage without having the protection of a long term trim) where with a long term trim (low octane map and octane number) will shift with the onset of knock and should reduce the severity of new knock events..

There's always the possibility you will suddenly get bad knock due to detonation, neither can protect you from that, you can only mitigate the level of damage you can do.. Without that low octane map, your basically falling off the highwire and missing the net..

 

So Malibu, I get what you are saying (and you do a very good job at explaining it too) but does that mean that the Mitsu ECU has the ability to "lean"?

 

"Learn"?

 

Jack gave a good analogy. I'll try to give a little more info for each of your questions again:

1. There really isn't a complete switchover between the Hi Octane and Low Octane maps. As the octane number in the ECU goes down, a weighted average of the two values for the same cell in each map is used.

For example, if your octane number is at 255, only your Hi octane map value will be used...100%(Hi octane value) + 0%(low octane value).

If your octane number has been lowered from knock counts above 6, and let's say that your octane number is now 230. Well, 230 is about 90% of 255. So, you will use 90% of the Hi octane value and 10% of the low octane value. Let's say the timing in your Hi octane map for a given cell is 18* and in the low map that value is 9*. You will use .9(18*)+.1(9*) = 17.1*.

If your octane number was right in the middle, or 127, then your timing would be .5(18) +.5(9) = 13.5*

If your octane number was 0, then your timing would be 9*, since it would use 100% of the low octane map value.

All of this depends on your octane number. If you search this forum, there is a thread by jcsbanks that describes the octane # behavior. I believe at 0-3 counts of knock, it increases, at 4-6 it stays the same, and at 7+, it lowers. But don't quote me on that.

2. Yes, with both maps the same timing will be pulled. The dual maps is more of a preventative method, as described in Jack's analogy. But, timing is still pulled with the maps the same...roughly 1* for every 3 counts of knock. But, since the maps can't correct for prolonged knock, then you will knock every time you have a problem, instead of the ECU learning and changing the octane value, preventing the knock in the first place.

3. I don't know what the scale for octane number is in EvoScan .97.

4. A higher octane gas can change the AFR if the specific gravity is different. For example, pump gas has a specific gravity of about .76. C16 has a specific gravity of about .73. So, you will run about 4% leaner with C16 than with pump, without changing your fuel maps.

5. Yes the ratio is based on mass, but since some higher octane gases have different specific gravities, they have different masses per volume.


Eric

 

Yeah "lean" as in the Subaru ECU. IIRC, there is an algorithm programmed into the Subaru ECU that enables it to avoid some knock events and to advance timing if conditions are favorable.

 

I think 6 knock counts the octane decreases because thats what happen to me.

 

^^^^6 knock counts decreased you octane # by how much. 1 point, 6 points? and are you using the logger that uses 100, or 255 as the 100% high octane #?
thanks

 

Okay I understand what you mean now.. No the Evo ECU doesnt ever advance timing past whats in the maps, its not programmed to do that.. Just to retard timing as knock events, or interpolate the value somewhere between from the high octane and low octane maps (If its not 100% (255) or 0%(0))

 

ya i want to know how many octane points does it drop by when you get say 6 counts of knock, cause if its only like 1 or 2 you have to knock like 300 times before you fully switch over to the low map, that seems like alot of knock for the motor to endure before the timing is where the low maps timing is.