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Old 06-18-2013, 12:55 AM   #1
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Default GAir changes drastically at 2k RPM?

So I've been messing around with my MS2V3 lovingly crafted by Reverant, trying to fine tune everything while I'm normally aspirated prior to going turbo. My latest issue has been heatsoaking causing the MAT to rise and the subsequent GAir adjustment leaning out my mixture too much. I've read the threads on this, I realize that optimal temp sensor placement will improve things, and I've tried various settings on the MAT correction table and MAT correction values.

My issue is that when I go back over my logs, GAir still seems to be pulling fuel out above 2000rpm no matter what my MAT corrections are. I attached one example of this where I am using the Gair-negating MAT corrections settings (the settings were initially posted by Braineack I think, it keeps GAir at around 100% no matter what the MAT). Here, my MAT is in the mid 90's, and you can see GAir stays around 100% whenever the engine is below 2000rpm, but whenever it goes above 2k it's like the MAT corrections turn off and GAir suddenly jumps to 95%.



I have other more dramatic examples where the engine is more heatsoaked with MATs in the 120s and GAir pulls out even more fuel when I get above 2k rpm. In all my searching, I have not found a setting that turns off the MAT corrections above a certain rpm like it seems to be doing for me, nor have I seen any mention of this in any posts. What am I missing? Any help is greatly appreciated.
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GAir changes drastically at 2k RPM?-99496v.png  
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Old 06-18-2013, 03:28 AM   #2
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This is normal.

Non-linear IAT correction is fully applied below 1200rpm, and then its tapered down gradually until 2K rpm, where no non-linear IAT correction is applied, and the usual gair correction (based on PV=nRT) is used.

I've found out over the years that the non-linear correction should only be used below 2000rpm where the airflow on the sensor is low enough to not provide reliable readings due to heatsoak; above 2000rpm it is not a problem. When non-linear correction was allowed above 2000rpm, the air-fuel ratio would change drastically between 3-4 pulls because of the air actually being heated. Hell, even one long pull (say 5th 60-140) would not have the same AFR start to finish due to the non-linear correction screwing everything up.
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Old 06-18-2013, 09:48 AM   #3
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I'm still using the stock airbox and stock NB temp sensor right now, figured I wouldn't bother with the GM IAT sensor until I put in the intercooler, piping, etc. With the stock sensor, it seems to take a while for temps to come down when it's heatsoaked, even when the car is moving and the engine revving. Does the temp on the GM IAT sensor come down a lot faster than the stock NB sensor when it gets good airflow going over it?
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Old 06-18-2013, 11:01 AM   #4
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Yes, quite a bit.
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