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A way to convert from Injector Pulse width to duty cycle?

Discussion in 'EFI Tuning Questions and Engine Management' started by Turbostangman, Jan 18, 2004.

  1. Turbostangman

    Joined:
    Jan 30, 2003
    Pretty much says it all. Does anyone know a formula to do this?
     
    Turbostangman, Jan 18, 2004
    #1

  2. my8950

    Joined:
    Jan 30, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    They are 2 different things...Duty cycle % is how hard the injector is working. Pulse Width is the amount of time the injector is open or on.
     
    my8950, Jan 18, 2004
    #2

  3. twinturbostang

    Joined:
    Jan 28, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    I believe duty cycle is just a ratio of the amount of time the injector is open vs. the amount of total time it can be open. This would be the amount of time between cycles for a single piston, or two revolutions of the crankshaft.

    So for instance, the available time at 6000rpm is 20ms. This is found by first dividing 6000 by 2 (since TWO revolutions of the crankshaft per ONE cycle). This is still in RPM units though (Revolutions Per Minute), so divide again by 60 (for seconds) = 50. Then it's just 1 divided by 50, which equals 0.020 seconds, or 20 milliseconds. And finally it's pulsewidth divided by available time. So say you've got a pulsewidth of 15ms, 15 / 20 = 0.75. So you are at 75% duty cycle.

    Keep in mind though, that this changes for whatever RPM you're at. If you're pulsewidth stays the same, duty cycle will actually go up as RPM goes up, because you have less and less time to inject the fuel.

    Brian
     
    twinturbostang, Jan 18, 2004
    #3

  4. Turbostangman

    Joined:
    Jan 30, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    Thanks Twin!! I knew it was a matter of on time vs dead time in relation to RPM. I just wondered if anyone had an online calculator for using a given PW and RPM and it would spit out Inj duty cycle. I'm too lazy to do all that math.....:D
     
    Turbostangman, Jan 19, 2004
    #4

  5. twinturbostang

    Joined:
    Jan 28, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    No problem! I'm sure someone has an online calculator to do it. But when you solve down all the math, it's a VERY simple calculation. Here ya go...

    (Pulsewidth * RPM) / 1200 = % Duty Cycle

    Pulsewidth is in millisecond units. So for example a pulsewidth of 10 ms at 6000rpm.... (10 * 6000) / 1200 = 50% duty cycle.

    That's all there is to it! :)
     
    twinturbostang, Jan 19, 2004
    #5

  6. Craig Smith

    Joined:
    Sep 17, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    That equation only hold true for a V8, don't forget! At 6000 RPM, a 6 cylinder engine has much more time to inject than an 8 cylinder. So technically the number of cylinders factors into the equation.

    I should make a little Excel deal that takes a couple variables and spanks out the number of your choice. That would be cool. :rockon:
     
    Craig Smith, Jan 19, 2004
    #6

  7. my8950

    Joined:
    Jan 30, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    Good deal then, thanks all others for clarifying!!! Learn something new every day!
     
    my8950, Jan 19, 2004
    #7

  8. twinturbostang

    Joined:
    Jan 28, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    Craig: It has nothing to do with the # of cylinders. We're talking duty cycle of each injector, which is PER cylinder. Whether you're talking 4, 6, 8 cylinders, they all have the same cycle time at 6000 RPM. So that doesn't even factor in. The only thing you have to watch is if you're doing this for a two stroke engine, in which case the firing cycle is once every revolution. Four stroke is of course once every TWO revolutions.
     
    twinturbostang, Jan 19, 2004
    #8

  9. Craig Smith

    Joined:
    Sep 17, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    :eek:

    Oops.

    Sorry about that, you are absolutely correct. My brain was focused on a slightly different issue that has more to do with the available time between TDC events of adjacent cylinders. But 6000 RPM is 6000 RPM and it doesn't matter how you slice it for determining injector duty cycle.
     
    Craig Smith, Jan 19, 2004
    #9

  10. twinturbostang

    Joined:
    Jan 28, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    Not a problem. :tu:
     
    twinturbostang, Jan 19, 2004
    #10

  11. Turbostangman

    Joined:
    Jan 30, 2003
    Turbostangman, Jan 19, 2004
    #11

  12. twinturbostang

    Joined:
    Jan 28, 2003
    A way to convert from Injector Pulse width ti duty cycle?

    Cool! [click: bookmark]

    That's a handy table! :)
     
    twinturbostang, Jan 20, 2004
    #12
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