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Thread: BPW and Injector math

  1. #16
    Super Moderator dave w's Avatar
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    Here is something I quickly put together.

    dave w
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  2. #17
    Fuel Injected!
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    Quote Originally Posted by dave w View Post
    Here is something I quickly put together.

    dave w
    Since I'm not very good with excel.....

    Can you put the BPW calculator in your previous post, this fuel pressure flow change calculation, and the IDC flow calculation all into one excel spreadsheet?

    [4 * IPW (ms) * RPM]/1200
    Last edited by chevmasta; 02-24-2013 at 08:39 AM.

  3. #18
    EFI GearHead ! EagleMark's Avatar
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    I've got about a bazillion hours into learning spreadsheets. Almost 13 hours into edits in this one recorded in the file.

    Special Thanks to Dave W at Old School EFI for sharing his BLM spreadsheets, they are all included.

    For evaluation only! I've tested till I'm blind and it all seems to work properly. Warning, spreadsheet on steroids! If it passes inspection I think it's worthy of GearHead-EFI.com name...

    EDIT: New upload with protection issue on Injector Duty Cycle fixed.
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  4. #19
    Super Moderator dave w's Avatar
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    Quote Originally Posted by EagleMark View Post
    I've got about a bazillion hours into learning spreadsheets. Almost 13 hours into edits in this one recorded in the file.

    Special Thanks to Dave W at Old School EFI for sharing his BLM spreadsheets, they are all included.

    For evaluation only! I've tested till I'm blind and it all seems to work properly. Warning, spreadsheet on steroids! If it passes inspection I think it's worthy of GearHead-EFI.com name...
    I'll try to review the above attached spreadsheet...I have excel not Open Office. See attached screen shot.

    dave w
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  5. #20
    EFI GearHead ! EagleMark's Avatar
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    Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.
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  6. #21
    Super Moderator dave w's Avatar
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    Quote Originally Posted by EagleMark View Post
    Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.
    Much better! I can see the formulas in the individual cells with the .xls file format.

    dave w

  7. #22
    Fuel Injected!
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    I have excel too.

    I tried plugging some numbers in but nothing changed. are these two not compatible in that way? (preface: imanidiot)

    ....and you just posted it.... LOL!

  8. #23
    Fuel Injected!
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    Thankyou for that sheet Mark.

    I've only tuned my truck.......but I do have a couple people interested in me helping their trucks out and that spreadsheet will be most helpful!

    It's really cool to have a community like this one. :)

  9. #24
    Super Moderator dave w's Avatar
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    Quote Originally Posted by EagleMark View Post
    Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.
    I've been challenged with the question on IPW. I noticed the attached spreadsheet is write protected for Injector Duty Cycle (IDC) MPFI vs TBI. To correctly calculate IPW TBI vs. MPFI (IDC) is required. So I'm wondering why IDC is write protected.

    dave w
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  10. #25
    EFI GearHead ! EagleMark's Avatar
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    I protected everything so people would not change the cells that were not in White! There is no password, in Open Office just click Tools, Protect Document and Sheet to turn off protection. I assume Excell is similar?

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  11. #26
    Super Moderator dave w's Avatar
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    Quote Originally Posted by EagleMark View Post
    I protected everything so people would not change the cells that were not in White! There is no password, in Open Office just click Tools, Protect Document and Sheet to turn off protection. I assume Excell is similar?
    The Excel message I posted states how to disable write protection. I was hoping to help others who might encounter the same write protection message.

    I'm wondering where the formula for injector bias was sourced from? Some TBI definitions don't show an injector bias ($85, $OD, $OE, $E6, $31 $61, $62)? I think $42 usually has 454 injector bias @ .276 and 350 injector bias @ .375? I'm wondering if changing injector bias will affect injector flow?

    dave w

  12. #27
    EFI GearHead ! EagleMark's Avatar
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    Added to the total BPW. used to compensate for injectors that open slowly. As the fuel pressure is increased the injector takes longer to open. If you add fuel pressure this should be increased.
    Injector bias is in $42, $85, $61 and all the older ECM that have a BPW/BPC. Notice these do not have Cubic Inch or any displacement or Injector size? It is calculated by engine size in liters / 8 so volume of one cylinder, divided by rate of injector at grams/second = vol/rate * 1461.5 = BPC
    Code:
    TBI 5.7L 61 lb/hr = 61.2 lb/hr $0D states injector size is 61 lb/hr
     Val = 1461.5  * (VOL/RATE)
     VOL  = Vol of 1 Cylinder in liters, (0.7125l)
     RATE = Injector flow in gms/sec
     5.7l = 7.71 gms/sec (61.2#/HR)
     (VOL/RATE) = 0.0924 l/gm/sec
     = BPW 135
    It is not in newer PCM like $0D which does not have BPW/BPC. The starting BPC is calculated by injector size and Engine displacement that those masks have.

    But there's much more to BPW/BPC that I have not figured out the math for yet!!! If you stick to the guidelines this is not an issue. But you know yourself and I and others have had this discussion on cheating and adding BPW/BPC for more fuel. My tests showed that to work to some extent but fall apart at higher RPM/Load if raised and I found out why. Injectors go static at about 150 BPW/BPC at 3600 RPM!!! Base Pulse Width is time injector is open compared to how much time is available at RPM, so back to why Duty Cycle is so important, Injector Pulse Width in percent of time open in M/Sec changes with RPM = time gets shorter. But if we could do the math we would find a direct correlation from Injector Duty Cycle to BPW/BPC.. constant.

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  13. #28
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    But if we could do the math we would find a direct correlation from Injector Duty Cycle to BPW/BPC.. constant
    Say this differently... what are you looking for? The BPC alone won't give you IDC because injector pulsewidth is a function of the air calculation. Are you trying to estimate how much the BPC can be adjusted without going static?

  14. #29
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by 1project2many View Post
    Are you trying to estimate how much the BPC can be adjusted without going static?
    Yes! There has to be a point where it is static... right? RPM...

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  15. #30
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    this would be my first guess for estimating where going static would occure:

    find RPM with highest injector duty cycle, let's say it's 75%.

    now, you know you can run up to 25% more fuel before you run into 100%DC, though you may go static before then, but for theoretical purposes, 100% is the target. take your BPC and multiply it by 1.25 (to make it 125% of it's original value), and then you SHOULD hit 100% DC in the otherwise identical condition, assuming the O2 sensor doesn't cause a significant reduction to base fueling.
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