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Thread: Newbie Question on Main Timing Tuning, +- BTDC/ATDC Reference

  1. #1
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    Newbie Question on Main Timing Tuning, +- BTDC/ATDC Reference

    Hi there HP land.

    I have tuned a few turbo cars, but I'm new to diesel. Well, pretty new. I'm starting to wrap my head around the concepts.

    I have read and I'm familiar with the idea of how a diesel combusts, SOI timing etc, but I'm having trouble determining the +- reference to BTDC/ATDC in HP tuners tables.

    It seems this is how the timing works, please correct me if I'm wrong:

    Main Injection Pulse: Negative numbers indicate a BTDC value. Positive numbers represent a ATDC value. -2* is 2* BTDC, +2* is 2* ATDC
    Pilot Injection Pulse: Value indicates how long the pilot pulse preceeds the main event. Not sure if it's supposed to be the pilot SOI or EOI
    Post injection Pulse: Time in us from the end of the man injection to the post SOI


    Comments??

    Thanks,

    Chay

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    Advanced Tuner MAIDENCR's Avatar
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    Negative number is ATDC....positive is BTDC
    Pilot timing(pre) is degre before main injection
    And post injection you simply remove it...

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    Pilot pulsewidth and post pulsewidth is the exact same thing as main pulsewidth, the length of time the injector is held open for that event. Pilot timing by default is set relative to main injection, so crank angle degrees before main injection for when pilot injection begins. If pilot overlaps into the main event the main event will push up the pilot event till there is a separation of 250us. Post timing by default is crank angle degrees after the end of main injection.

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    Awesome thanks guys. You can convince yourself either way if you try hard enough lol.


    So if I took an example (Made up), where I'm at 2400RPM, 2500us duration, and timing is +8, then:

    2400rpm = 14400deg/sec; 2500us is 36* Of Injection


    +8 is 555.55 us BTDC, for a % of 22.2 BTDC. Pulse ends at 1944ms, or 28* ATDC



    But if timing was -2, then we inject from 2* ATDC to 38* ATDC



    If a guy wanted to inject more fuel, it might be wiser to bump fuel rail pressure rather than inject later, or leave fuel rail pressure alone, increase both duration and some timing, all in an effort to avoid later combustion which has limited effect.



    Seem Right?


    Thanks,

    Chay

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    Advanced Tuner MAIDENCR's Avatar
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    Tuning is a mix of timing, rail pressure and duration

    My tune timing is mostly 60btdc/40atdc and since i do some sled pull and spin engin to 4k rpm i also limit my main injection to 23deg atdc when it rev over 3500rpms
    03 cummins,175% flux injectors,dual cp3,s467.7/83 1.00
    Nv5600 with valair triple disc clutch

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    Quote Originally Posted by cfoss1000 View Post
    Awesome thanks guys. You can convince yourself either way if you try hard enough lol.


    So if I took an example (Made up), where I'm at 2400RPM, 2500us duration, and timing is +8, then:

    2400rpm = 14400deg/sec; 2500us is 36* Of Injection


    +8 is 555.55 us BTDC, for a % of 22.2 BTDC. Pulse ends at 1944ms, or 28* ATDC



    But if timing was -2, then we inject from 2* ATDC to 38* ATDC



    If a guy wanted to inject more fuel, it might be wiser to bump fuel rail pressure rather than inject later, or leave fuel rail pressure alone, increase both duration and some timing, all in an effort to avoid later combustion which has limited effect.



    Seem Right?


    Thanks,

    Chay
    Not quite what you are thinking. Everything you do has an effect on when the combustion starts and the period over which combustion occurs. Increase pressure, you may need to reduce injection timing. Reduce pressure you may need to increase timing. Increase duration, you may need to increase timing. Your goal is to get the middle of combustion time to occur approximately a couple degrees after top dead center. Everything effects it. Your pilot event, ambient pressure, ambient temperature, fuel pressure, duration, timing. There is a large amount of factors that affect ignition delay and the characteristics of the combustion process. Many people shoot for a 50/50 timing split, putting the injection duration 50% before top dead center and 50% after top dead center, this will not optimize where your combustion, the important part, is occuring during the engine cycle.

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    Advanced Tuner MAIDENCR's Avatar
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    Quote Originally Posted by Jim P View Post
    Not quite what you are thinking. Everything you do has an effect on when the combustion starts and the period over which combustion occurs. Increase pressure, you may need to reduce injection timing. Reduce pressure you may need to increase timing. Increase duration, you may need to increase timing. Your goal is to get the middle of combustion time to occur approximately a couple degrees after top dead center. Everything effects it. Your pilot event, ambient pressure, ambient temperature, fuel pressure, duration, timing. There is a large amount of factors that affect ignition delay and the characteristics of the combustion process. Many people shoot for a 50/50 timing split, putting the injection duration 50% before top dead center and 50% after top dead center, this will not optimize where your combustion, the important part, is occuring during the engine cycle.
    How we can know when the combustion is happening?? If the 50/50 rule isnt good

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    Load cell dyno and map optimization, find the peak torque producible for each cell in the maps. But still everything affects everything even right down to fuel quality. One tank of fuel could produce worse torque than the previous tank. Won?t be able to get everything absolutely perfect, there?s always compromises but you can get everything very close. I don?t know any big name tuner that uses the 50/50 rule.

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    Advanced Tuner MAIDENCR's Avatar
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    this is what I will do soon...hope I will have great result
    since engine is quieter at idle with timing atdc….at cruising speed you think it should be less btdc like at idle....like 40/60 or something???
    03 cummins,175% flux injectors,dual cp3,s467.7/83 1.00
    Nv5600 with valair triple disc clutch

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    ignore timing splits is my advice. out of gear idle is a different ball park and will depend on many factors just like everything else in tuning does. go for what makes it idle smoothly without rattle and without haze. some setups may require timing down to like -6*

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    Advanced Tuner JaegerWrenching's Avatar
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    Jim, Say you're getting close timing wise, or so you think, what are good increments to creep up to your MBT? .2* changes?

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    .2-.5 if you feel you?re really close, keep in mind there is always interpolation going on between cells in a map, so it?ll take a bit of finessing in a quadrant of the area you are working in. It?ll always be more biased towards one cell but the surrounding cells do have an effect on the cell it?s biased towards.

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    Here's a sample of how surrounding cells affect each other.

    timing sample 1.png

    In the above photo, I picked a random spot in my timing table and picked a random theoretical logged rpm and torque of 1622rpm and 360Nm. I built in formulas to do the interpolation to a high accuracy of what you would actually see in a data log and highlighted the heaviest biased cell timing is being pulled from. At 1622rpm and 360Nm, it's coming to a final timing value of 4.79*BTDC.

    timing sample 2.png

    In the above photo I change the timing value at 1600rpm/375Nm from 4.31*BTDC to 4.81*BTDC, resulting in a final timing of 5.10*BTDC.

    timing sample 3.png

    Putting timing at 1600rpm/375Nm back to 4.31*BTDC and changing timing at 1700rpm/300Nm from 5.88*BTDC to 5.50*BTDC has resulted in a final timing value of 4.77*BTDC.

    timing sample 4.png

    Now putting timing at 1700rpm/300Nm back to 5.88*BTDC and change timing at 1700rpm/375Nm from 5.47*BTDC to 5.8*BTDC results in a final timing of 4.85*BTDC.

    Hopefully this demonstrates how all cells affect each other through the interpolation of the maps that the ECM does.
    Last edited by Jim P; 05-13-2019 at 04:50 PM.

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    Say you want to raise timing at that 1622rpm/360Nm point by 0.2*to have a final timing of 4.99*BTDC, I could raise the most heaviest biased cell in the interpolation by 0.32* which would result in the final timing of 4.99*BTDC.
    timing sample 5.png

    Or I can manipulate 3 cells to bring final timing up to 4.99*BTDC.
    timing sample 6.png

    Of course changing the cell that the interpolation is most heavily biased towards is going to have the largest effect on how it changes the final timing.
    Last edited by Jim P; 05-13-2019 at 05:04 PM.

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    Advanced Tuner MAIDENCR's Avatar
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    To really know if you are close timing wise we need a dyno??

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    Quote Originally Posted by MAIDENCR View Post
    To really know if you are close timing wise we need a dyno??
    Quote Originally Posted by Jim P View Post
    Load cell dyno and map optimization, find the peak torque producible for each cell in the maps. But still everything affects everything even right down to fuel quality. One tank of fuel could produce worse torque than the previous tank. Won?t be able to get everything absolutely perfect, there?s always compromises but you can get everything very close. I don?t know any big name tuner that uses the 50/50 rule.
    Unless you have the capability of watching and timing the combustion process as they do in a controlled science lab...

    Another thing to keep in mind is after dyno tuning you will want to run it throw the ropes on the street and could potentially need to make adjustments street tuning for driveability. A vehicle will or can behave differently on the street versus on a dyno.

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    on a dyno you WILL see if a change is negatively affecting torque in a spot you are working on. I know I can't feel the difference of 50Nm of torque.

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    Something to keep in mind when on a dyno doing map optimization is when watching your torque and you are raising up timing, say at 1600rpm/45mm3 you start at 5*BTDC and increment timing up 1* at a time, let?s say at 8* you at a peak torque of 275Nm then it above 8* it falls back down again. You keep raising timing by 1* and by 13* you?ve hit 278Nm and it kind of plateaus afterwards. Take into consideration cylinder pressures. The higher you go with timing the higher the cylinder pressures you will have, especially with higher fuel amounts. High cylinder pressures is what causes headlift. So weigh whether that extra 5* is worth the extra 3Nm of torque for that extra cylinder pressure that will be coming along with it.

  19. #19
    Advanced Tuner MAIDENCR's Avatar
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    The 3nm more dont worth it ahaha
    Will see june 20...i should go on dyno

  20. #20
    Advanced Tuner JaegerWrenching's Avatar
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    Jim great explanation as always. I've noticed with my ecu and data logging it seems it's good at almost anticipating where it's going timing wise. Say it's a WOT pull, 980tq 2400rpm i'm at 12* in my current cell, 15* at 2600rpm upcoming cell and it actually seems to lean more towards the upcoming cell rather than surrounding or current cell. So i'd see a value of 13.8* current timing instead of being 12 or 12.5* But that was making observations prior to knowing what you just said. But i was paying attention to surrounding cells trying to figure out why it was doing that. I was also having my timing be slightly lower than commanded just recently, so this info is awesome, Thanks Jim!