ATTN: All TunerCat users. WOT AFR values. - Third Generation F-Body Message Boards

TRAXION · 11-17-2000, 02:04 PM

First, a big thanx to the gmecm mailing list and Bob R. for lending the info to allow me to draw all of these conclusions. I sent a letter to TunerCat indicating the following...

Quote:

TC,

I believe that I have uncovered an inconsistency with regard to the $8D TDF for the tables ...

PE %Change to Fuel/Air Ratio vs. Coolant Temp.
PE %Change to Fuel/Air Ratio vs. RPM

I attempted to calculate the Air/Fuel ratio for a stock AUJP bin (1990 Camaro IROC-Z, 5.7L, Automatic, 3.23 gears) for 80deg C. and 4000RPMs. The PE for Coolant Temp shows 22.7% in TunerCat and the PE for RPM shows 7.8% in TunerCat. Applying these percentages against the stoichiometric 14.7AFR yields 10.22AFR [according to (14.7 - ((22.7+7.8)/100)*14.7))]. The value of 10.22 is incorrect. The true AFR can be calculated according to the following formula (as retrieved in the ANHT_HAC.PDF) ...

WOT AFR = 6553.6 / (((TBL L8617 + TBL L860D + 128) * 445) / 256)
WOT AFR = 6553.6 / (((148 + 58 + 128) * 445) / 256)
WOT AFR = 11.3

TBL L8617 is the decimal value located in the PE %Change to Fuel/Air Ratio vs. RPM table for a specific RPM.
TBL L860D is the decimal value located in the PE %Change to Fuel/Air Ratio vs. Coolant Temp. table for a specific degree C.

My Diacom readings prove this to be correct because an AFR Requested value of 11.3 is shown at 4000RPMs at a coolant temp close to 80deg C. So, this formula is true to form.

The ANHT_HAC.PDF also presents another way to calculate the WOT AFR ...

WOT AFR = 14.7 / (LAMBDA C + LAMBDA W)
LAMBDA C = Decimal value for PE %Change to Fuel/Air Ratio vs. Coolant Temp. which has been modified by dividing by 256.
LAMBDA C = TBL L860D / 256
LAMBDA W = Decimal value for PE %Change to Fuel/Air Ratio vs. RPM which has been modified by dividing by 256 and adding 0.5
LAMBDA W = (TBL L8617 / 256) + 0.5
SideNote: This means that a 0% change in AFR would mean a TBL L860D value of 0 and a TBL L8617D value of 128.

Using our original values from the first equation we can calculate the AFR again...
WOT AFR = 14.7 / ( (TBL L860D / 256) + (TBL L8617 / 256) + 0.5) )
WOT AFR = 14.7 / ( (58 / 256) + (148 / 256) + 0.5) )
WOT AFR = 14.7 / (0.227 + 1.078)
WOT AFR = 11.3 (same as before)

The main problem is the display of the %Changes for PE. I am not sure if this can be fixed or not. I used TnrEditor to try to rectify the problem myself but can't seem to make it work. I understand WHY you did it the way that you did. It makes perfect sense according to the LAMBDA C and LAMBDA W equations above. But, it doesn't work when you are thinking of percentages.

As an example lets assume a 22.7% TunerCat PE change for coolant at 80deg and NO % TunerCat change at any RPMs ...
WOT AFR = 6553.6 / (((128 + 58 + 128) * 445) / 256)
WOT AFR = 12.0
The %Change in this case is: 18.37% even though TunerCat reads 22.7%

As another example lets assume a 0% PE TunerCat change for coolant at 80deg and a 10% TunerCat change at 4000 RPMs ...
WOT AFR = 6553.6 / (((154 + 0 + 128) * 445) / 256)
WOT AFR = 13.37
The %Change in this case is: 9.05% even though TunerCat reads 10%

Sincerely,
Timothy Siford

So - make sure that you are calculating your AFRs using the formula given above and in the ANHT_HAC and not what you would think would be the case. You will need to use a Hex Editor to extract the decimal values from the Bin or you can use the following equations ...

To calculate the decimal value in the BIN using a TunerCat PE WOT vs RPM value ...
TBL L8617 = (TC Value + 50) / 0.390625

To calculate the decimal value in the BIN using a TunerCat PE WIT vs Coolant Temp value ...
TBL L860D = (TC Value / 100) * 256

Just wanted to pass this information along. Again - big thanx to the GMECM mailing list for opening the right doors.

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 after installing Hooker LT Headers and reducing weight.
-=ICON Motorsports=-
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