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Thread: 2004.5 Cummins Total fuel Timing graph

  1. #1
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    2004.5 Cummins Total fuel Timing graph

    Im trying to wrap my head around a diesel timing formula to calculate a total timing graph for a datalog as well as individual graphs for pilot, main, post. What would be the formula which ties all 3 together and would also show a total percent before or after tdc? Id like to use the datalog graphs themself to make adjustments to my tune instead of having to rely on excel etc. Is it even possible? Thanks

  2. #2
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    Waste of time man, just not how things work.

  3. #3
    Advanced Tuner MAIDENCR's Avatar
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    Personnally depending on injector...but with my 100hp injector in cruise area i was at 100% btdc.....at high load with the pulse i had (2600us) i was at 60-65% btdc at 3500+rpm
    Now with my 250hp at cruising im at 30% bdtc(to keep smoke/haze down) and at high load its 75-80% btdc....
    Pilot arround 20? btdc
    Feel free to ask if you need mor info
    03 cummins,175% flux injectors,dual cp3,s467.7/83 1.00
    Nv5600 with valair triple disc clutch

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    To the original question, there is no formula to add all 3 timing values together to correlate with total fueling. Total fueling is the combined value of pilot, main and post. Main fueling is commanded fueling minus pilot and post fueling. Pilot and post events are used for emissions control, NOx, SOx, etc. Pilot is also used to reduce combustion rate of rise, thus reduce combustion in cylinder peak pressure which results in a reduction of the classic diesel rattle of a mechanical injection diesel sound.

    There is absolutely zero formula to tell you where timing should be at for any engine or build. The ultimate goal for optimum tuning is for the peak pressure from the main event to occur a few degrees after top dead center. Without custom head and pressure transducers, etc. etc. it?s just a crap shoot to actually hit that.

    You can have two dead identical trucks and put the same tune on both and one truck can hate it while the other loves it. That?s where the beauty of custom tuning comes in, you can fine tune to what the vehicle in question likes, just gotta find what it likes. With street tuning, you gotta listen to what your engine is telling you, listen to what the turbo is telling you, gauge how the response of the truck feels.

    There is no one solution fits all. There are some general rules of thumb that are generally considered to be safe but depending on factors like intended use, altitude, build, you could potentially take those general rules of thumb and toss in the garbage. Things like more boost means more power isn?t necessarily true. Depending on factors you could make more power with less boost.

    The hard truth is, there is no magic numbers and formulas for tuning.

  5. #5
    Advanced Tuner MAIDENCR's Avatar
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    Agree with jim
    03 cummins,175% flux injectors,dual cp3,s467.7/83 1.00
    Nv5600 with valair triple disc clutch

  6. #6
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    Sounds good. So what im gathering is that pilot main and post are all the same event just broken apart for tuneability. What im trying to figure out is what everyone is talking about when they say "i have x degrees of timing at lets say 1000 rpm for wot. Where are they getting that definite number from to tell people? Im not asking what number is best im trying to figure out where the number itself is derived from, (main, pilot, post or a ratio of the 3 or is it just the main that they are talking about). Hope that makes sense. Lol

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    A general rule of thumb for timing that is considered by many to be safe in the upper fuel quantity and upper rpm range is 1 degree for every 100us of duration. This is derived from testing on the dyno.

    Depending on individual circumstances, what may be considered safe may fall outside of that. An example would be very high altitude operations.

    One thing that can be guaranteed is there are ZERO definite numbers for timing.
    Last edited by Jim P; 10-15-2020 at 07:27 PM.