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Thread: How is injector timing calculated?

  1. #1
    Tuner blkscooby's Avatar
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    How is injector timing calculated?

    I have played around with the EOIT boundary to reduce or remove the raw fuel mixture being sent out the exhaust valve with my new cam (has 8* overlap).

    Now I am trying to be scientific about the values I really need based on my new valve timing events. I have my cam card so I know what they are.

    My question is not so much what target angle to use, but how the ECM calculates it based on the 3 tables- Boundary, Normal ECT, and Normal RPM.

    In the stock tune I know that GM targeted to inject all fuel before the intake valve opened for better atomization.

    1. The way I understand the tables to work is Boundary + ECT - RPM = actual EOIT. Now after further review, I'm not sure this is correct. How is EOIT calculated?

    2. Also, what do the crank angles referenced from? Is 0* TDC of the compression stroke? Or something else? If it was 0* TDC compression, then the stock injection boundary of 520* would place it at the tail end of the intake stroke, which does not match GM's approach to finish injection prior to the start of intake stroke.

    Once I understand these 2 questions, then I can calc where my EOIT settings need to be.

  2. #2
    Senior Tuner DSteck's Avatar
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    1. Boundary - ECT - RPM

    2. 0* is TDC between compression and combustion.

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  3. #3
    Tuner blkscooby's Avatar
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    Thanks Steck! I was confused by the descriptions in HPT for each table.

  4. #4
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    what values did you use to remove the raw fuel smell? i think i ended up with around 30

  5. #5
    Tuner blkscooby's Avatar
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    I'm around 60-65* retarded now.

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    i understand how injector timing can help with idle smell, but could there be any performance gain at part-wot?


    edit: Well i guess now that i think of it as IDC goes up the injector timing gets less and less important.
    Last edited by Blingole; 11-17-2012 at 07:07 PM.

  7. #7
    Senior Tuner DSteck's Avatar
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    If you have huge injectors, you can play with it more.

    Don't forget kids, EOIT is the end of the shot. The beginning of the shot should begin when the exhaust valve shuts.

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  8. #8
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    so now we need to log injector ms at the specific rpm and convert to degrees?

  9. #9
    Tuner blkscooby's Avatar
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    Quote Originally Posted by DSteck View Post
    If you have huge injectors, you can play with it more.

    Don't forget kids, EOIT is the end of the shot. The beginning of the shot should begin when the exhaust valve shuts.
    Right, still working on it.

  10. #10
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by carlrx7 View Post
    so now we need to log injector ms at the specific rpm and convert to degrees?
    Keep in mind that display injector pulse width is BEFORE the voltage offset and short pulse are included.

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  11. #11
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    Quote Originally Posted by Blingole View Post
    i understand how injector timing can help with idle smell, but could there be any performance gain at part-wot?


    edit: Well i guess now that i think of it as IDC goes up the injector timing gets less and less important.
    there is a power difference on getting the timing right, and there is an importance on getting it back in line as well. regardless of engine rpm and {if you're under 100% idc} there is still a valve closing and injector dead time. the window gets smaller and smaller though
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  12. #12
    What is the purpose of the makeup pulses and do they occur before or after the injection timing boundary?

    I believe the main objective in EOIT tuning is to get the last of the fuel leaving the injector through the intake valve before it closes. So not only do you need to finish spraying fuel before the valve closes, you also need to account for the time it takes for the fuel to travel from the injector through the valve.

  13. #13
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    Dave,

    Ever think about making an Injection Calculator? I know the disel guys have one.

    http://www.hptuners.com/forum/showthread.php?t=29684

    Just something simple,

    input injector info and cam info. boom!

    -Carl

  14. #14
    Senior Tuner DSteck's Avatar
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    Already did.

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  15. #15
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    cheater!

    guess this is what happens when an engineer starts messing with his own car
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  16. #16
    Senior Tuner DSteck's Avatar
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    You guys that have been trying to figure it out are on the right track. It's actually pretty straight forward to do. It just takes a little algebra (well, trig/dynamics too I suppose).

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  17. #17
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    they just have a one up on myself. they have the op/cl degree events where as, i do not
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  18. #18
    Senior Tuner DSteck's Avatar
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    Without the exact cam events, it's guessing for sure.

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  19. #19
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    yep. my guessing game is actually going fairly well right now. since, thats really all i can do at this point in time. aside from tearing the front cover off
    The most hated, make the most power.
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  20. #20
    Quote Originally Posted by DSteck View Post
    You guys that have been trying to figure it out are on the right track. It's actually pretty straight forward to do. It just takes a little algebra (well, trig/dynamics too I suppose).
    I would love to hear more. Any chance of an explanation?