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Do negative numbers add more fuel... in the table "WOT %change to AFR vs RPM" table? IE if I had a setting of -3.9% at 4800 rpm, that changes the AFR from 14.7 to 14.12. Therefore a lower AFR means the ECM will add more fuel to get that ratio. Please correct me if I am wrong. I just want to make sure I understand this properly before I make changes. ------------------ Best ET 14.413 @95.57 without pulling valve covers or manifolds. Also with stock 2.77 rear end!!! |
<font face="Verdana, Arial" size="2">Originally posted by MikeT 88IROC350: in the table "WOT %change to AFR vs RPM" table? IE if I had a setting of -3.9% at 4800 rpm, that changes the AFR from 14.7 to 14.12. Therefore a lower AFR means the ECM will add more fuel to get that ratio. Please correct me if I am wrong. I just want to make sure I understand this properly before I make changes. </font> -3.9% would lean the engine. The larger the AFR the leaner. 14.7 is normal cruise, idle 16.5 would be a lean cruise AFR 12.5 would be a WOT AFR |
There's also another parameter affecting PE AFR entitled "WOT AFR % Change vs Coolant Temp" in Tunercat. Check out Traxion's post on how to calc PE AFR from these parameters. https://www.thirdgen.org/messgboard/...ML/000273.html |
Why would -3.9% LEAN the engine, if I am going from 14.7 to 14.1 AFR? Or do I have my math wrong here?? I realize that higher AFRs are leaner. I just checked out that post. Guess I got some homework to do. But how do the negative numbers play into this table? |
<font face="Verdana, Arial" size="2">Originally posted by MikeT 88IROC350: Why would -3.9% LEAN the engine, if I am going from 14.7 to 14.1 AFR? Or do I have my math wrong here?? I realize that higher AFRs are leaner. I just checked out that post. Guess I got some homework to do. But how do the negative numbers play into this table?</font> -x%, means taking away fuel. +x%, means adding fuel |
Remember ... TunerCat is just an editor and it displays values however TC set it up. TC set it up such that NEGATIVE numbers mean less fuel. Negative numbers will raise the commanded AFR (leaner mixture). If you want to calculate the REAL AFR value then you need to determine the actual modifier (which can be derived from the hex value) and then use the appropriate formula. I know that probably sounds a little difficult but its not that bad. Check out the link presented by one of the previous posters. Tim ------------------ TRAXION's 1990 IROC-Z Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8) All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust. -=ICON Motorsports=- Moderator: PROM board at thirdgen.org |
Thanks fellas. Things are making sense now. I realize that you cannot just take the numbers in the table and apply them to the AFR. I checked out the formulas to calculate AFR based on the 2 tables. But when there really is a negative % in the table, do you input the negative in the formula as well? I kind of wondered about these -% from the ARAP bin. I have -3.9% from 3600 all the way to 6400. I believe that my car does not pull as hard when I punch it since I put these ARAP values in the WOT tables. If the engine is leaner at WOT condition, it might not make as much power. I may switch back to my GM/ADS values. I would think you would want more fuel in the PE mode, but I suppose it all depends on what the ENGINE wants. |
Remember ... the values that you are looking at in TunerCat ARE NOT the real HEX values that are being entered into the actual binary file. These percentages are only for your viewing pleasure. AFR is calculated through use of the WOT PE Coolant *modifier* and the WOT PE RPM *modifier*. Although you may be looking at a negative number in TunerCat .... these values are not negative in the actual binary file. You'll need to acquire the ACTUAL modifiers in order to calculate AFR. They say that a picture is worth a thousand words. Hopefully this will help. I created my own program to calculate all of the possible AFRs as well as a view into the modifiers. For me, this makes changing the AFRs easy since I can change the AFR directly by specifying a AFR. I can also change the modifiers directly if I wish to work with the Hex values. http://www.xecu.net/timsiford/afr.jpg Tim ------------------ TRAXION's 1990 IROC-Z Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8) All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust. -=ICON Motorsports=- Moderator: PROM board at thirdgen.org |
That graphic definitely turns on some light bulbs. I started on a spreadsheet of my own, basically a set of lookup tables, and I would input the desired temp and rpm. But when I saw your 2-dimensional table, that is a better way to go. I don't have access to the modifier in the hex code, so I will be using the formulas to calculate the modifiers. Hopefully this is an accurate method. This is cool stuff!!!! ------------------ Best ET 14.413 @95.57 without pulling valve covers or manifolds. Also with stock 2.77 rear end!!! |
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