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Thread: Short pulse adder x axis, include offset at 14v?

  1. #1
    Tuner homebuilt's Avatar
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    What is the "x axis" of Greg's short pulse adder data?

    I created a spreadsheet that can derive the gm format injector table values from the Published Ford values so that I could get the values in GM format for a lower fuel pressure to test effects on fuelIng error at low pulse widths (80 lb injectors).

    However, when checking the calculations the short pulse adder (SPA) data from Greg wouldn't correlate with the Ford data unless I used the BPW + Offest value to look up the SPA. I thought that he GMs use the BPW to look up the SPA. Then add the offset.

    I input the data as it was explained in the video. But looking more closely now I noticed in his spreadsheet the lookup row is labeled "x axis value". I don't expect that his derivation is wrong. My calculations agree only if I included the offset in the value that is looked up in the SPA table.

    So where am I going wrong with this calculation?

    I do plan on sharing my spread sheet, minus Greg's data of course, once this is sorted out.
    Last edited by homebuilt; 08-14-2012 at 06:38 PM.

  2. #2
    Tuner homebuilt's Avatar
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    To state this simply, does anyone know what pw is used for looking up the short pulse adder? Is this the BPW + the offset? Please use some numbers to show the process.
    Last edited by homebuilt; 08-14-2012 at 06:38 PM.

  3. #3
    Senior Tuner DSteck's Avatar
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    www.injectordynamics.con

    Go read some of the tech articles. They show you where different values come from and how GM and Ford data are developed from the same graph. This might shed some light on the situation for you.

    Very cool to make a spreadsheet that converts it over. Good luck!

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  4. #4
    Tuner homebuilt's Avatar
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    Thank you Dave, is it bad that I've already read everything that ID has published and I have been corresponding with Paul and I still haven't found the answer.

    Maybe the engineer in me is making this more complicated than it is.

    I will read again to see if I missed anything.

    Could you walk through an example short pulse calculation?

  5. #5
    Tuner homebuilt's Avatar
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    Ok, I read all of the materials again. Great reading but no "light bulb" moments for this question unfortunately.

    I attached a plot to explain my question better.

    As you can see, you will get totally different SPA values if you use the raw linear BPW instead of the pulse width with the offset at 14v included.

    And by my math, only the latter agrees with the total IPW you would get if you calculated it using the Ford format data.

  6. #6
    Senior Tuner eficalibrator's Avatar
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    You are probably on the right path here... One interesting point is the magnitude of errors here. The max correction on the LU80 shown above is 0.3ms, with a maximum delta between the two cases of 0.15ms. Shot to shot variation on these injector is pretty much this big, and combustion stability is also of a similar magnitude. This means a relatively small difference in delivered fuel mass or measured lambda either way.

    On the SD60, the numbers are even smaller, so the errors are just about negligible either way. The more linear the injector is (stock LS3, SD60, or ID850 for example) the less role Short Pulse Adder plays in final fueling.

    I'm in the middle of revising my injector data sheets as a result of empirical testing and SAE flow bench testing. There may be a slight shift in some datasets in the near future as a result. More importantly, the part to part variation seems to greatly outweigh all of this anyway on production Siemens injectors. I'm seeing that non-flow matched sets can have variability that is orders of magnitude greater than the shift in SPA data shown, so it almost makes the general characterization not worth it for random samples. Does this mean I don't want exact characterization data anymore? Not a chance. But it does make me also want to verify that any set of injectors I get are both completely characterized AND dynamically flow matched.

  7. #7
    Tuner homebuilt's Avatar
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    Hi Greg,

    Thank you for your input.

    I'm well convinced that with the availability of better injector options since my previous investment I would be best to swap them out.

    On the math question above, I can make the plots match exactly if I add the offset for 14v to the raw linear base pulse. Using that value to look up the short pulse adder makes the math work. Butttt, everyone is telling me that it is the raw linear pulse value that is looked up in the short pulse adder table.

    What is the "x-axis" value that we are entering the adder relationship against? Milliseconds of what?

  8. #8
    Advanced Tuner HartRod's Avatar
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    Gentlemen, thanks for a great discussion and I apologize for bringing up an old thread, but were these issues ever addressed? Greg do your DVD's have the new data from your testing? Maybe a better question to ask, "If these SD80 injectors are so hard to tune, should I get a different brand?" Thanks in advance.
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  9. #9
    Senior Tuner eficalibrator's Avatar
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    1) All current samples of SME-DVD-1 data disc now ship with the latest file (rev3). It's a very small change, but I wanted it to be right on the money so I went ahead and included it a while ago. If you have the older version, don't sweat it as your data works out to be damn close anyway.
    2) SD80's are a bitch to tune, even with the right data. You'll notice that the min PW spec from Siemens/Continental/FRPP is pretty large. They simply aren't that happy trying to consistently deliver the very small fuel masses required for stoich idle at low airflow. The data in my DVD simply models the "best fit" to this very non-linear behavior, but the part-to-part variation is even greater. I have seen only minimal success with the SD80s, even with perfect data from that exact set. I've had much better results using the SD60's, which are good to ~1000hp at 4bar fuel pressure. If you really need 80's, I'd seriously look at the Injector Dynamics ID850s instead. Their low end behavior is significantly more predictable.

  10. #10
    Senior Tuner DSteck's Avatar
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    SD80s suck. Shot to shot and injector to injector just isn't consistent. They'll run an engine, but there's a marked difference in using properly matched injectors.

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  11. #11
    Advanced Tuner HartRod's Avatar
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    Quote Originally Posted by eficalibrator View Post
    1) All current samples of SME-DVD-1 data disc now ship with the latest file (rev3). It's a very small change, but I wanted it to be right on the money so I went ahead and included it a while ago. If you have the older version, don't sweat it as your data works out to be damn close anyway.
    2) SD80's are a bitch to tune, even with the right data. You'll notice that the min PW spec from Siemens/Continental/FRPP is pretty large. They simply aren't that happy trying to consistently deliver the very small fuel masses required for stoich idle at low airflow. The data in my DVD simply models the "best fit" to this very non-linear behavior, but the part-to-part variation is even greater. I have seen only minimal success with the SD80s, even with perfect data from that exact set. I've had much better results using the SD60's, which are good to ~1000hp at 4bar fuel pressure. If you really need 80's, I'd seriously look at the Injector Dynamics ID850s instead. Their low end behavior is significantly more predictable.
    Thanks for the info Greg.

    Quote Originally Posted by DSteck View Post
    SD80s suck. Shot to shot and injector to injector just isn't consistent. They'll run an engine, but there's a marked difference in using properly matched injectors.
    I got my injectors new (flow matched) through FIC. they said I could send them back if I couldn't get them tuned. Please make a recommendation for which injectors I should get. My setup is here:

    http://www.hptuners.com/forum/showth...S1900-1968-C10

    Thanks,
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  12. #12
    Senior Tuner DSteck's Avatar
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    Injector Dynamics. They're the only ones who dynamically match and not just full flow match. You also get real data for them (not copied, stolen, or made up data like the others).

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  13. #13
    Senior Tuner LSxpwrdZ's Avatar
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    SD 80's def are a bit of a pita to dial in. However after tuning quite a few sets you can get a general idea of what it needs to operate the car correctly. I will say that not a single car has ended up with the exact same SPA or offsets just mainly due to variations in the injectors. On engines not consuming much fuel at idle or free reving at extremely light load you have to really play with the minimum pulse and transiet fuel mass to make them behave normal.

    Having done nearly all ID's injectors one time or another, they are in a different league as far as injectors are concerned.
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