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Thread: BPW and Injector math

  1. #46
    EFI GearHead ! EagleMark's Avatar
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    Well I didn't change any numbers to make it work up until Roberts injectors and fuel pressure to make it work. But here's how I came up with others

    Part of the calculation given to us is in hacks, volume in liters of one cylinder liter/rate of one injector in grams per second. But I did increase precision by going 10 number past decimal point. Does not work at .1 need .1111111111
    TBI V8 engine 1461.5 = 1 injector firing four cylinders

    PFI V6 engine 487.166 = 3 injectors firing 3 cylinders, so one third the original 1461.5

    PFI V8 engine 365.375 = 4 injectors firing 4 cylinders, so one fourth the original 1461.5

    I suspect a SFI engine would be back to 1461.5 firing one cylinder per injector?

    Back to TBI. Nothing was changed! These injector flows were all found in hacks and come out to 13PSI fuel pressure:
    61 lb/hr (61.2#/HR) 7.71107029 gms/sec
    76lb/hr (75.55#/HR) 9.519139876 gms/sec
    80lb/hr (80.50#/HR) 10.1428293847 gms/sec
    If you use those injector numbers the Grams/Second are accurate for one injector.

    AND correct engine liters it comes out accurate to one cylinder liter!
    5.7L 350 engine = 5.7329775012L / 8 for one cylinder.
    7.4L 454 engine = 7.4390737152L / 8 for one cylinder.

    Numbers come out perfect to BPC in bin...

    All I have for 3.1L engine is 3.5 bore and 3.25 stroke = 3.1217081827L / 6 for one cylinder.

    If the the 60V6 engines ran 43.5PSI at full pressure all the time? What would the difference in flow be with vacuum to without vacuum? Seems like the flow/pressure/differential is the only thing in question for the calculation? 207 is pretty close to 224 BPC?

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  2. #47
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    Quote Originally Posted by RobertISaar View Post
    also, the 60V6 engines ran 43.5PSI at full pressure(until 99, i think, in 2000, they bumper up to ~52 or 55, i forget which)... pressure dropped from there with vacuum.
    43.5 at no vacuum, they run a vacuum referenced FPR.
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  3. #48
    EFI GearHead ! EagleMark's Avatar
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    207 out of 224 is the best I can do? Wait? Is there any multipliers or for BPC? Like some do for EGR? What is EGR BPC?

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  4. #49
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    with the MPFI V6 stuff, there is no "EGR off BPC" and a table for when EGR is active like what is present in a few masks, there is only the table.

    at 0% EGR, 224.
    at 12.8% EGR, 187. stays at 187 from 12.8-25.4%, probably because EGR never really gets commanded above ~7% at most. almost perfectly linear change from 0 to 12.8%.

    there are 3 tables that are multipliers to the BPC table result, one is vs baro, one is vs MAP/baro ratio, one is vs calculated intake runner temp. they interact with each other.... oddly.

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  5. #50
    EFI GearHead ! EagleMark's Avatar
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    That was my first impression... then came...

    But looking at it airflow multiplier at 105 baro comes up to 0, then starts at 219 BPW Inverse... still pretty close to 217 I came up with.

    If you do 95 baro and .25 you add 5.6 to 219 and get your 224...

    Whats the BPW Offset vs BPW do?

    BPW OFfset to battry voltage should be a zero at running voltage? How the heck are you supposed to figure that out? There's no Constqant to start with?

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  6. #51
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    the inverse table is simply a multiplier for accounting for estimated intake runner temp airmass correction, i just never entered the equation(the one GM supplied was.... useless)

    the way those all interact with A1:

    BPC vs %EGR of airflow value is looked up, saved twice.
    airflow multiplier vs MAP/baro ratio is looked up and multiplied with one of the BPC vs EGR% values, value is then saved.
    airflow multiplier vs baro is looked up and multiplied with the same modified BPC vs EGR% value.
    then the unmodified BPC vs EGR% value is pulled and added to the modified value and saved.

    that value is used for the basis of the speed-density calculation(i refer to it as "airflow", but it's not really)

    so, that value and the target AFR get mixed in interesting ways and form the "fuel required" value.
    that value then gets VE correction.
    that value then gets MAP correction.
    that value then gets intake runner temp correction.

    now the value is the base pulse width before O2/closed loop and injector offset correction.



    so, those 4 tables i posted about are ACTUALLY used as an adder for the BPC value, they can never be subtractive. honestly, i'm amazed it works as well as it does, but i still want to scrap it all for a real speed-density derived airflow / fuel required value.
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  7. #52
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    Those are factory tables? Is MAP / BARO ratio table actually MAP / BARO in code? Is that the leftmost table, which has entries from 0 to .5? And is that value frequently calculated based on current MAP readings or is it a correction that's only updated if BARO is updated?

    Also, is there a coolant temp correction or an inverse AFR multiplier?

    Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9
    Last edited by 1project2many; 02-28-2013 at 07:00 AM.

  8. #53
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by 1project2many View Post
    Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9
    That could be another hack!

    But the purpose here was not to figure out how once tuned, it was to avoid it by calibrating a tune in the first place. I still think theres a clue in BPW (now known as correct BPC) as far as RPM. Seems a smaller number BPC will rev higher, increase pressure, recaculate BPC and number gets smaller was my first clue, then seeing $85 7.4L BPC at 142? Higher then other BB with bigger injectors at BPC 134... well it's hitting %85 Injector Duty Cycle at 3500 PRM and BLM go lean.

    I think BPC of 135 is 13.5 Msec

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  9. #54
    EFI GearHead ! EagleMark's Avatar
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    Here's some convincing numbers. In another thread a 7.4L engine with 74 (75.55)lb/hr injectors and BPC set to 142 from factory.

    He is having BLM issues at higher RPM and reported 7.05 Msec at 3600 RPM. Using the formula in calculator
    TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
    7.1 M/sec, 3600 RPM set to TBI is 85.2% Injector duty cycle.

    If you use the MPFI formula
    MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200
    on his BPC of 142 which I still believe is M/sec so 14.2 at 3600 RPM guess what? Same 85.2% Injector Duty Cycle!

    Is it because of TBI injector firing strategy compared to MPFI strategy that this works? What cuts BPC in half for injector duty cycle? 2 injectors? Firing? DRP? Could also be the reason these systems go Async after it runs out of Sync fuel for higher load needs?

    If you use a lower BPC of 125 = M/sec 12.5 at 3600 RPM it goes down to 75%...

    To get to 5000 RPM and stay under 85% Injector Duty Cycle you need a BPC of 102! Seems to be working...

    So it's looking like calculating BPC for higher fuel pressure is not only correct, but the lower BPC is also needed for higher RPM?

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  10. #55
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    If he's at 85% IDC then the injector is too small. BPC, VE, BARO, CTS correction... all work together to come up with injector "on time." If the BPC is wrong, then during tuning the VE tables will "automagically" get adjusted wrong in the other direction and make up much of the difference. At the end of the day, tuning for AFR and best timing, no matter how you play with the variables you'll hit the same wall. 85% IDC. It's just robbing Peter to pay Paul.

    BPC may work out to a time value. You can use Excel to see required BPC for a specific engine size, VE, and AFR. This one also helps visualize IDC.
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  11. #56
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    Quote Originally Posted by 1project2many View Post
    Those are factory tables? Is MAP / BARO ratio table actually MAP / BARO in code? Is that the leftmost table, which has entries from 0 to .5? And is that value frequently calculated based on current MAP readings or is it a correction that's only updated if BARO is updated?

    Also, is there a coolant temp correction or an inverse AFR multiplier?

    Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9
    all factory values.

    MAP/baro ratio is exactly as it sounds, MAP and Baro get loaded, then divided, then the result of that is the MAP/baro ratio. yes, it's the leftmost table.

    coolant temp correction / inverse AFR multiplier?c

    oolant temp is accounted for in the intake runner temp calculation, where it's used with IAT, airflow and a couple of other values to estimate airmass temp by the time it gets into the cylinders.

    inverse AFR... that might be the rightmost table loaded, using the equation given by GM, it gaves values in *Kelvin, which was pretty useless to me once i looked at the code and determined the table value was simply used as a multiplier.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  12. #57
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by 1project2many View Post
    If he's at 85% IDC then the injector is too small. .
    What's strange about 7.4L $85/$D8 bins is BPW was 134, then later 142! I beleive this was the year 7.4L changed from 80 to 76 lb/hr injectors. This is also the mask that was $85 BCC Axxx that was all superceeded to $D8 Bxxx.

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  13. #58
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    Quote Originally Posted by EagleMark View Post
    That could be another hack!

    But the purpose here was not to figure out how once tuned, it was to avoid it by calibrating a tune in the first place. I still think theres a clue in BPW (now known as correct BPC) as far as RPM. Seems a smaller number BPC will rev higher, increase pressure, recaculate BPC and number gets smaller was my first clue, then seeing $85 7.4L BPC at 142? Higher then other BB with bigger injectors at BPC 134... well it's hitting %85 Injector Duty Cycle at 3500 PRM and BLM go lean.

    I think BPC of 135 is 13.5 Msec
    Quote Originally Posted by EagleMark View Post
    Here's some convincing numbers. In another thread a 7.4L engine with 74 (75.55)lb/hr injectors and BPC set to 142 from factory.

    He is having BLM issues at higher RPM and reported 7.05 Msec at 3600 RPM. Using the formula in calculator
    TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
    7.1 M/sec, 3600 RPM set to TBI is 85.2% Injector duty cycle.

    If you use the MPFI formula
    MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200
    on his BPC of 142 which I still believe is M/sec so 14.2 at 3600 RPM guess what? Same 85.2% Injector Duty Cycle!

    Is it because of TBI injector firing strategy compared to MPFI strategy that this works? What cuts BPC in half for injector duty cycle? 2 injectors? Firing? DRP? Could also be the reason these systems go Async after it runs out of Sync fuel for higher load needs?

    If you use a lower BPC of 125 = M/sec 12.5 at 3600 RPM it goes down to 75%...

    To get to 5000 RPM and stay under 85% Injector Duty Cycle you need a BPC of 102! Seems to be working...

    So it's looking like calculating BPC for higher fuel pressure is not only correct, but the lower BPC is also needed for higher RPM?
    Quote Originally Posted by 1project2many View Post
    If he's at 85% IDC then the injector is too small. BPC, VE, BARO, CTS correction... all work together to come up with injector "on time." If the BPC is wrong, then during tuning the VE tables will "automagically" get adjusted wrong in the other direction and make up much of the difference. At the end of the day, tuning for AFR and best timing, no matter how you play with the variables you'll hit the same wall. 85% IDC. It's just robbing Peter to pay Paul.

    BPC may work out to a time value. You can use Excel to see required BPC for a specific engine size, VE, and AFR. This one also helps visualize IDC.
    Quote Originally Posted by EagleMark View Post
    What's strange about 7.4L $85/$D8 bins is BPW was 134, then later 142! I beleive this was the year 7.4L changed from 80 to 76 lb/hr injectors. This is also the mask that was $85 BCC Axxx that was all superceeded to $D8 Bxxx.
    Mark is talking about this thread:
    http://www.gearhead-efi.com/Fuel-Inj...y-math-7060-85

    This is where I'm at 85% IDC. Which seems weird considering the truck engine is mostly stock minus headers and an exhaust. Fuel pressure has ben adjusted from 12psi to 16psi.
    I'm currently going to try to raise my BPC to 150 and retune my VE table and see where I end up.....up top. Mind you im not "that" lean. Up top a BLM of 131 (BUT im only at 58% throttle.......I just realized). In PE mode I sure would think it would run out of fuel...........but I don't have any knock counts at WOT thank God.

    Mark,
    Just for clarification. I'm using the $85 mask with a BANC.bin
    Should I be using the $D8 mask becuase of the superceed? Will it make a difference?

  14. #59
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by chevmasta View Post

    Mark,
    Just for clarification. I'm using the $85 mask with a BANC.bin
    Should I be using the $D8 mask becuase of the superceed? Will it make a difference?
    Stick with $85, there's a few issues with $D8 tables I never fixed when I found all Axxx bins were superceeded to Bxxx bins, although all I have seen they are identical except $D8 has governer paremeters. It would take some work but they need to be combined.

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  15. #60
    Fuel Injected! gregs78cam's Avatar
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    Just to double check the Advanced $0E that I am using, what should the conversion/equation be?
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