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Thread: Question on PE/WOT air fuel ratio

  1. #1
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    Question on PE/WOT air fuel ratio

    So I am playing around with and still learning how the Gen 5 engines tuning works. One of the questions I have is derived from a new change I made to my setup.

    Car is a 17 Camaro SS M6 with a Procharger D1SC at 10psi. I have catless headers into a AWE Touring axleback system. Car has the full LT4 fuel system (LPFP, HPFP, injectors, and all of the LT4 fuel lines). As of now the car makes 640rwhp on E35-E40. When the PC setup was put on the car the shop put on a Alky Controls dual nozzle meth injection system. Originally the car made 650rwhp on 91 with the meth inj system, then I swapped in all of the LT4 stuff and had the car retuned by another tuner, he fixed tons of things wrong with the previous tune. The car runs great with zero issues at all, never sees any knock at all.

    So after spending some time on the phone with the owner over at Alky Controls I went the route of re-purposing the meth inj system to use it as it was intended, to cool the air charge down. I used a DSX IAT/Baro break out kit and moved the IAT into the intake about 2" past the throttle body. I am running a 50/50 mix of VP Racing M1 methanol and distilled water.

    The logs look great, fuel pressure on the low side is 73psi and the high side is a little over 26xx psi. The A/F was commanded for .83 Lambda and came in at .80 so it is a little rich. Normally I know to correct that is a minor adjustment with the MAF calibration (airflow vs. frequency) table. Here is wherein my question lies.

    Is there a PE/WOT Lambda ratio for gas and then for E85? I guess my question is how is commanded Lambda for gas and then E85 determined? In this case with me using the meth inj to cool the intake charge down it is throwing the commanded A/F off and making the car richer. So do I just adjust that thru the MAF calibration or is there somewhere else I need to be making corrections at?

    Todd

  2. #2
    Senior Tuner Ben Charles's Avatar
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    Make the PE leaner so Tq model stays more accurate..

    That or adjust VT tables so commanded Tq stays accurate

    Couple of ways to skin the cat

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    Assuming you want the easiest path first, you would lean out the PE table to compensate for the added fuel via meth. But you might have to adjust your torque coefficient ratio table if you go too low of a value in the PE table because then your torque model will be off. If you look at the stock coefficient table you see the numbers are above 1.0 during PE commanded equivalence ratio. Typically they are just over 1 in the stock PE area, then fall below 1 if you go above or below this equivalence ratio, and are 1.0 during stoich. If you go too low with your equivalence ratio where the coefficient table references a number below 1 you could have unexpected changes to your torque model. So you will need to adjust this if necessary. If you change the MAF values up top it will also change the final torque calculations as airmass is a large part of the calculation the ECU uses to determine torque output.

    Your other question for commanded lamda. There is a stoich table that is typically a sliding scale based on ethanol content in the tune. Before E10 and E85 all tunes said stoich was 14.7:1 for gasoline. With E10, stoich is actually 14.1:1. And then it changes to a lower value for E85 on a sliding scale based on total ethanol content. That said, we are going to assume for this example that we are running E10 and stoich is 14.1:1 as referenced by the ECU. The math is simple though and reverse-able. Let's say you want to command .85 Lamda at WOT.

    stoich = 14.1
    WOT desired AFR: 12:1 (approx .85 lambda for E10)

    If you take 14.1 and multiply by your desired lamda of .85 you get the following AFR (14.1 x.85) = 11.985:1 AFR. This is the math so that you can work out an Air Fuel Ratio to Lambda if you're still not familiar with working with everything in Lamda values.

    So lets to go the ECU and the PE table. Stoich for E10 is known to be 14.1:1 by the ECU. Then in your PE table you have 1.155 commanded at WOT. The math for that is backwards of the above. 14.1/1.155 = 12.2 AFR commanded. Now you just need to work that into Lamda. All you do is divide commanded AFR by stoich. 12.2/14.1 = .865 Lambda.

    Essentially you will need to use the value the ECU is reading for Stoich to do this math for any other fuel blends other than E10. But if you were running E10 and Lambda was reading .80 then your AFR is 14.1 x .80 = 11.28:1. If you have true E85 in the tank then the stoich is 9.8:1 so your AFR is 9.8 x .80 = 7.84 AFR. This obviously is why we all should be tuning in Lambda now because .80 Lambda on E85 is still .80 Lambda on E10 even though the AFR's are way different.

    Just a note, your tuner may have tuned it a bit rich to safeguard in the event you run out of meth during a WOT event. The ECU may pull out enough timing to save some engine parts if its running rich and the meth runs out. Otherwise if you go from a great AFR on meth, then run out of meth and go lean the ECU may not be able to pull out enough timing and boom. There really isn't a whole lot of power to be had between .80 lambda and .85 lambda so don't go chasing tiny amounts of power over this. The only time I would worry about running as lean as possible is when you're at the track and you know your meth tank is full. I would leave the tune richer on the street. But thats just my personal opinion.
    I've tuned a few things...

  4. #4
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    Quote Originally Posted by TriPinTaZ View Post
    Assuming you want the easiest path first, you would lean out the PE table to compensate for the added fuel via meth. But you might have to adjust your torque coefficient ratio table if you go too low of a value in the PE table because then your torque model will be off. If you look at the stock coefficient table you see the numbers are above 1.0 during PE commanded equivalence ratio. Typically they are just over 1 in the stock PE area, then fall below 1 if you go above or below this equivalence ratio, and are 1.0 during stoich. If you go too low with your equivalence ratio where the coefficient table references a number below 1 you could have unexpected changes to your torque model. So you will need to adjust this if necessary. If you change the MAF values up top it will also change the final torque calculations as airmass is a large part of the calculation the ECU uses to determine torque output.

    Your other question for commanded lamda. There is a stoich table that is typically a sliding scale based on ethanol content in the tune. Before E10 and E85 all tunes said stoich was 14.7:1 for gasoline. With E10, stoich is actually 14.1:1. And then it changes to a lower value for E85 on a sliding scale based on total ethanol content. That said, we are going to assume for this example that we are running E10 and stoich is 14.1:1 as referenced by the ECU. The math is simple though and reverse-able. Let's say you want to command .85 Lamda at WOT.

    stoich = 14.1
    WOT desired AFR: 12:1 (approx .85 lambda for E10)

    If you take 14.1 and multiply by your desired lamda of .85 you get the following AFR (14.1 x.85) = 11.985:1 AFR. This is the math so that you can work out an Air Fuel Ratio to Lambda if you're still not familiar with working with everything in Lamda values.

    So lets to go the ECU and the PE table. Stoich for E10 is known to be 14.1:1 by the ECU. Then in your PE table you have 1.155 commanded at WOT. The math for that is backwards of the above. 14.1/1.155 = 12.2 AFR commanded. Now you just need to work that into Lamda. All you do is divide commanded AFR by stoich. 12.2/14.1 = .865 Lambda.

    Essentially you will need to use the value the ECU is reading for Stoich to do this math for any other fuel blends other than E10. But if you were running E10 and Lambda was reading .80 then your AFR is 14.1 x .80 = 11.28:1. If you have true E85 in the tank then the stoich is 9.8:1 so your AFR is 9.8 x .80 = 7.84 AFR. This obviously is why we all should be tuning in Lambda now because .80 Lambda on E85 is still .80 Lambda on E10 even though the AFR's are way different.

    Just a note, your tuner may have tuned it a bit rich to safeguard in the event you run out of meth during a WOT event. The ECU may pull out enough timing to save some engine parts if its running rich and the meth runs out. Otherwise if you go from a great AFR on meth, then run out of meth and go lean the ECU may not be able to pull out enough timing and boom. There really isn't a whole lot of power to be had between .80 lambda and .85 lambda so don't go chasing tiny amounts of power over this. The only time I would worry about running as lean as possible is when you're at the track and you know your meth tank is full. I would leave the tune richer on the street. But thats just my personal opinion.
    ok, that helps some.

    The car was tuned without meth by the current tuner. It was tuned for .83 Lambda. I saw the PE tables for gas and for alcohol when I was looking the other night. I want to say instead of a tiered table like the stock tables are setup, the tables are now fixed at 1.15 for gas and I think 1.22 for alcohol setup across the entire table. Based on the guy over at Alky Controls the 50/50 mix of methanol and water should be a 0 additive and shouldnt make it richer or leaner, but it seems like it is affecting it some as the logs before I put the meth inj back online was at the commanded .83 and now they are richer for sure.

  5. #5
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    Quote Originally Posted by Ben Charles View Post
    Make the PE leaner so Tq model stays more accurate..

    That or adjust VT tables so commanded Tq stays accurate

    Couple of ways to skin the cat

    So the current gas PE table is set to 1.22 across the entire table, the alcohol is set at 1.16. i am not sure if this is correct though, the info tab shows anything more than 1 is richer. On the stock tables the Gas is closer to 1 than the Alcohol, so I am wondering why the gas table is set at 1.22 and the alcohol is at 1.16, to me it seems they should be the other way around, yes?

  6. #6
    Advanced Tuner mbray01's Avatar
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    Quote Originally Posted by sneakyws6 View Post
    so the current gas pe table is set to 1.22 across the entire table, the alcohol is set at 1.16. I am not sure if this is correct though, the info tab shows anything more than 1 is richer. On the stock tables the gas is closer to 1 than the alcohol, so i am wondering why the gas table is set at 1.22 and the alcohol is at 1.16, to me it seems they should be the other way around, yes?
    pe is a multiplier, equivalency ratio. It multiplies stoich by your pe number. You will sometimes end up with weird pe numbers if your airflow models are not correct, or sometimes an engine wants a "fat" 93 tune, but a "lean" e85 tune, or vise versa. When properly done, these are just numbers and multipliers, basically a means to an end.
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  7. #7
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by Sneakyws6 View Post
    So the current gas PE table is set to 1.22 across the entire table, the alcohol is set at 1.16. i am not sure if this is correct though, the info tab shows anything more than 1 is richer. On the stock tables the Gas is closer to 1 than the Alcohol, so I am wondering why the gas table is set at 1.22 and the alcohol is at 1.16, to me it seems they should be the other way around, yes?
    Gas
    14.7 / 1.22 = 12.05 afr

    E85
    9.85 / 1.16 = 8.49 afr

    12.05 / 8.49 = 1.42

    1.0 / 1.42 = .70

    get my drift?

  8. #8
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    Quote Originally Posted by Higgs Boson View Post
    Gas
    14.7 / 1.22 = 12.05 afr

    E85
    9.85 / 1.16 = 8.49 afr

    12.05 / 8.49 = 1.42

    1.0 / 1.42 = .70

    get my drift?


    Yes, that helps as well. I found an online conversion table for stoich. If Lambda is commanded at .84 it would give me a 8.2:1 for E85 and 12.35:1 for gas. That means based on the formula you just posted that the gas tune is slightly rich current at 12.05 vs a commanded of 12.35. The E85 based on the PE table is is 1.16 which is 8.49 afr which comes out to .87. The logs shows I am actually at .80 or 7.81:1 so that means I need to make an adjustment to the PE table for the alcohol, correct?

  9. #9
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    Do you have a flex fuel sensor? If so, the PE tables are being blended based off alcohol percentage.
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    Yes, the car has a FF sensor. Current E is at E35.

  11. #11
    Senior Tuner Higgs Boson's Avatar
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    If you are not getting commanded fueling then you need to adjust your MAF as long as your fuel pressure isn't dropping and/or your injector pulse width isn't going past about 6ms.

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    Low side is at 73psi at 6500rpm, high side is almost 2700psi and injector duty is 5.5ms.

  13. #13
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    Quote Originally Posted by Higgs Boson View Post
    If you are not getting commanded fueling then you need to adjust your MAF as long as your fuel pressure isn't dropping and/or your injector pulse width isn't going past about 6ms.

    So question on re-scaling MAF this way. So when I make changes in the airflow zones that need the correction based on the current E ratio I am at, then down the road lets say I put all gas in the tank. Does changing the MAF scaling this way not throw off the fueling for the pure gas or pure E85?

  14. #14
    Senior Tuner Ben Charles's Avatar
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    No Bc the stoich ratio defines fuel per given alcohol content, therefore of fuel model dialed in will work correct at any alcohol/gas level

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    I'd just lean out the PE tables until you get your desired final AFR. Otherwise you have to remap your VVE and MAF tables to include the meth spray.

    Or just run richer, which is probably safest as if you have a problem with the system, it will start target a safe AFR.


    Either way, if you run out of meth or your meth concentration changes, the stock ECU has no way of knowing and in open loop it will always cause a fueling change.

  16. #16
    Senior Tuner Higgs Boson's Avatar
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    If you have to lower your MAF or edit your PE table in order to keep from running out of fuel pressure or injector PW then you will go lean, if you compensate for that by spraying meth then you are "meth dependent" which is, IMO, a dangerous game.

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    Advanced Tuner mbray01's Avatar
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    There is a lot that goes into tuning these for proper fueling. I see so many vehicles that come to me that the owner was told they are out of fuel, so they cant go any further without "upgrades." 9 times out of ten, thats not the case. Injection timing plays a huge factor in fueling, yet is rarely properly re calibrated. Commanded fuel pressures, both low side and high side are rarely changed for the mods done to the vehicle. I have seen 25-30 reduction in fuel demand just by properly calibrating the proper tables. When they are properly calculated, not only does the fuel demand decrease, but power usually starts climbing as well. I have reverted more meth kits than i can count from supplemental fueling, back to air temp control, like they are intended, and got a happier engine, and a happier customer
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