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Thread: Rail pressure and timing

  1. #1
    Tuner in Training
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    Rail pressure and timing

    If I begin to adjust rail pressures will that effect my timing? My enitial thought is no, because all we are doing is inject more fuel volume in the same amount of duration.

    Not sure why but messing with my timing intimidates me.

  2. #2
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    Yes it plays a role in timing. If you are commanding 100mm3 at 100mPa it takes 1840 microseconds to inject that 100mm3 of fuel. Now if you increase pressure to 110mPa it 1740 microseconds to inject that same amount of fuel. It doesn?t inject the same amount of fuel in the same amount of time if you increase or decrease fuel. It will change where in crank angle degrees your injection ends. Increasing and decreasing pressure also affects things like in cylinder pressure and heat and atomization of the fuel that with the change in crank angle degrees of where the injection ends plus other factors it can throw your beginning of injection out of place from where it should be for optimum results.

  3. #3
    Oh man, Timing is where all the fun is! At 130-140mm3 and 2000rpm, put timing at 8* then at 130-140mm3 and 3000rpm put timing at 18 or 20*, do a linear function between them, then smooth the table. This is assuming you're still at stockish to 2200uS duration. This will pep the truck right up.
    I've found 2200uS, 22* timing and 24k Rail to be a great 70hp 150tq tune. Runs clean and tows great. That's my go to when someone wants a tow tune.
    06 SCLB. ATS stage 6, ATS Twin cp3, s369sxe, Fass 220, Hamilton 188/220, 110# springs, DDP 220's, ARP 425's, Big valve head, .40 over, 12v rods, balanced rotating assembly, Efi-Live etc.. 770hp 1380tq Tenacity Tuning

  4. #4
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    Thanks Jim and Dom. Appreciate the support you guys offer to the forum!
    After looking at the factory timing map and comparing it to dom’s suggestion. I realized these trucks came primarily with negative timing. Why is that? What is the purpose/benefits of it?
    Also Jim I’m beginning to play around with your timing calculator�� Thanks again

  5. #5
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    Your welcome. Sorry the timing calculator tables are rotated to match hp tuners tables, I keep meaning to get to reworking it but got so much on my to do list. Eventually it?ll happen. Just keep in mind the calculator is more for a visual representation of injection cycle, like how many crank angle degrees it?s spread over, when it begins, when it ends. There is no magic number for where your timing must be at. Again, there is NO magic number. Some people are hard dead set on 50/50 split or whatever and insist on using the calculator to get things like a 50/50 split or 60/40 split or whatever, do not get tied up in this mindset.

    The stock tuning you see has mainly to do with emission standards of that time.

  6. #6
    The negative timing does help a lot with smoke control as well. I use a lot of negative (ATDC) timing in the spool up range of the map, it will keep smoke down while putting heat into the turbine to help spool the turbo. The 04.5-07 pistons are arguably the worst of the cummins pistons for smoke.
    06 SCLB. ATS stage 6, ATS Twin cp3, s369sxe, Fass 220, Hamilton 188/220, 110# springs, DDP 220's, ARP 425's, Big valve head, .40 over, 12v rods, balanced rotating assembly, Efi-Live etc.. 770hp 1380tq Tenacity Tuning

  7. #7
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    doesn?t take a whole lot on the 04.5-07 to start producing smoke

  8. #8
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    Is it safe to run 48% split on my entire map for my base map? Then eventually adjust the low load and low rpm side of things as I go?

  9. #9
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    My basic plan at the moment is to smooth my rail pressure map. Leave the duration alone (possibly a bump in the lower right corner) then imput to a calculator @48% and see where I'm at. I have already changed some limiters for fuel and rpm.

  10. #10
    I would leave the cruise and low end stuff where it's at. 48% at cruise isn't going to be enough timing for optimal fuel mileage. If and when I use a calculator it's only to set timing in the top end. Smooth out the table and then do the calculator for the top end and see where it puts you.
    06 SCLB. ATS stage 6, ATS Twin cp3, s369sxe, Fass 220, Hamilton 188/220, 110# springs, DDP 220's, ARP 425's, Big valve head, .40 over, 12v rods, balanced rotating assembly, Efi-Live etc.. 770hp 1380tq Tenacity Tuning

  11. #11
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    Start with stock, raise timing a few degrees in a small spot and observe effects and how it runs in that spot. Lower timing below stock a few degrees in the exact same spot and observe the effects and how it runs. Work your way through different spots getting it to where you like how it runs. Just go through the process with rail pressure, timing, etc till you get what you like and it runs good. Throw the timing calculator away. It does NOT tell you where timing needs to be except for where YOU tell it to be. It will not tell you the right amount of timing needed for x sized injectors at x amount of pressure with x sized turbo and the list can go on and on.

  12. #12
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    Thanks guys! I will plug away at it for a bit. One quick question, is their a faster way to flash the ecu? It takes my laptop 10min.

  13. #13
    No sir, the CM848 takes forever to flash.
    06 SCLB. ATS stage 6, ATS Twin cp3, s369sxe, Fass 220, Hamilton 188/220, 110# springs, DDP 220's, ARP 425's, Big valve head, .40 over, 12v rods, balanced rotating assembly, Efi-Live etc.. 770hp 1380tq Tenacity Tuning

  14. #14
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    Yep, flash time is what it is.

  15. #15
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    Quote Originally Posted by Jim P View Post
    Start with stock, raise timing a few degrees in a small spot and observe effects and how it runs in that spot. Lower timing below stock a few degrees in the exact same spot and observe the effects and how it runs. Work your way through different spots getting it to where you like how it runs. Just go through the process with rail pressure, timing, etc till you get what you like and it runs good. Throw the timing calculator away. It does NOT tell you where timing needs to be except for where YOU tell it to be. It will not tell you the right amount of timing needed for x sized injectors at x amount of pressure with x sized turbo and the list can go on and on.
    This is the best piece of advice for timing. I have tried used timing calculators and values that big tuners use on a stock truck and swear by with absolutely awful results, there's just too many factors at play to warrant a "Perfect timing number". Every single engine will like different timing values even if they were built on the same day by the same guy using the exact same parts.

  16. #16
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    In my tune on my 03....all the cruise area (1000rpm and over/65mm3 under)is around 100% btdc....bottom left of table is on megative side to help spool up and bottom right(high rpm/load) is arround 60% btdc
    But 04.5-07 engine are different...almost always close to 0 or minus side

  17. #17
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    Everyone is always wanting to use percentages before top dead center, forget that. Every truck likes something different from the next, everyone?s setup is different, everyone?s operating conditions are different. What works well on one truck doesn?t always work well on another of the same build.