8.Lug

Seeing as I'll go through 5+ tanks of gas between events, it doesn't make sense to run hi-test all the time, so I run 87 in the meantime. Well I'm getting ready to build the engine - nothing crazy, most likely stay with the OEM 10:1 CR - but it will definitely require tuning and I would like to be able to continue this arrangement.

matts

I'm kinda new to all of this so I may be thinking wrong here, but tune the high table for your 87 octane and then copy it to the low table. Put your existing high table (that you've already got where you want?) numbers back into the high table. You should have both high and low tuned at that point.

The only problem I see is if you're running 87, and your ecm has put you into the low table, and you get some real knock it doesn't have anything to reference at that point. It already thinks it is in the safe zone. I'm not sure if they computer will continue to pull timing even if you're 100% in low table?

ChopperDoc

Tune the spark to run on 87. The PCM will always use the high table if you are not in SD. Take your new high table, copy it to the low table and pull out at least 5 degrees, if not more across the entire table. Reference a stock table and pull similar numbers. Not doing this will result in your PCM learning the knock over time (that will happen if not tuned to 87) and be added to "knock learn factor." Knock learn goes from 0-1, where 1=low octane table will be used, and 0=high octane. Anything between will be biased. Say your high octane is 20, and low octane is 10 and knock learn is 0.5. This would mean your PCM will set timing at 15, halfway between the tables.

Just tune it to run 87 with no knock, then set the low octane at least 5 degrees less, if not 10 in the higher rpms. That's up to you and your engine.

gametech

iTrader: (1)

Add up the difference in price between 93 and 87 times how many gallons of gas you use in a season. Find the difference between that and the cost of even one blown ringland. Then decide if this path is really even worth your time. Some of these discussions remind me of people who trade in a perfectly good car for one that costs 30k$ more because it gets 5mpg better mileage.

ChopperDoc

I agree completely with this. I was just offering the solution in the safest manner possible, or at least what I would do if it was my car. There is no way however, that I will ever be running 87 on my engine. I'm pushing it just on 93. I have too much money invested into it to take chances on cheap gas.

truckdoug

iTrader: (25)

i ran 87 in my stock L59 for couple years. would ping like a ************ hauling anything unless it dropped timing like 5* basically everywhere. IME even the "low compression" motors dont like anything but 92+ and even then the pisswater we get in the PNW for a "winter blend" will ping.

kingtal0n

iTrader: (1)

https://forum.hptuners.com/showthrea...l=1#post307136

ChopperDoc

Skip to 17:00 and it is explained very clearly.

ChopperDoc

If you have a knock learn of 1.00, then you have some issues with knock. I had a 98 pcm that used to show this as 1.00, couldn't get it to use the HO table at all in CL. After clearing up a MASSIVE amount of false knock, and tuning the sensors on race gas, it's 0.0. Not sure that the forum you cited is accurate. You know, it's a forum, just like this one, and people can be wrong. I never see knock learn be anything but 0.00 in my logs, and it uses HO on mine and every other car I've dealt with... well, unless it's knocking that is.

kingtal0n

iTrader: (1)

another one then
https://forum.hptuners.com/showthrea...k+learn+factor

i see threads with both, good catch, gotta pay attention

another one
https://forum.hptuners.com/showthrea...k+learn+factor
I even double triple checked with them because I wanted to be sure

ChopperDoc

Seems like there is some very conflicting information here. I have had no problems with knock at all and mine remains at 0. However when I had a lot, it was up at 1.0. Could also be partially caused by speed density though.

It's very odd that in the video you see it climb (as I have myself witnessed) as knock occurs. Strange indeed.

Off to check some logs... lol.

kingtal0n

iTrader: (1)

My logs say 1.00 and I am pretty sure Im getting all my juices

Im in SD w/ a 411 computer which I thought would default to low octane table but does not appear to have done so.

brandon6.0

iTrader: (32)

Yes a 411 should run solely off the lower timing table in SD mode. But i think some of the upgrade OS have the ability to keep the high octane table while in SD mode.

lanebaumann

Yes the upgraded OS for most PCMs lets you retain high and low octane spark map functionality.