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Thread: Max speed in spark advance control

  1. #1
    Senior Tuner
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    Sep 2008
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    Max speed in spark advance control

    In the 2000 LS1 PCM, what is the purpose of the "max speed" constant. Stock it is set to 43 mph, and the note says "This value is the speed required to disable the main spark tables"...why would you want to disable the main spark table? I don't understand.

  2. #2
    Advanced Tuner
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    Feb 2006
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    great question. i'd like to hear this one too. mine is at 4 mph,but then it has another box that adds 5mph to the four to revert to the main tables ????

  3. #3
    If the TPS is above the thresholds the Main Table is active

    If the TPS is below the threshold and if you are below this speed then the idle spark tables will be used (assuming the TPS is also less than the threshold).

    If TPS is below but speed is above the threshold, then Main table is used.

    in code form:

    if (TPS < thresh && MPH < thresh)
    Idle Spark
    else
    Main Spark
    I count sheep in hex...

  4. #4
    Senior Tuner
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    Oh alright, thank you for the info, I appreciate it.

  5. #5
    I was looking at my tune and it was set at 10mph but looking at a handful of other tunes and they are set at 250 or 255mph.

    This is the Main Spark Advance table

  6. #6
    Tuner in Training
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    May 2008
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    Still learning alot of the tuning myself. Maybe there's bucking or surging and some tuners disable the drop to idle timing. They just use the main spark to eliminate that variable. This is a guess of course!
    98 TA
    06 1500hd cc 4x

  7. #7
    Senior Tuner LSxpwrdZ's Avatar
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    I usually set this to ~250mph on most tunes because if you are moving and you let off the throttle sometimes if it still uses the main spark table the higher ignition timing will cause the car to idle high, but by raising this speed you basically are telling the computer to go off the idle spark table if the throttle is closed while the car is still or moving.
    James Short - [email protected]
    Located in Central Kentucky
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  8. #8
    Tuner in Training
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    Are you saying that raising this only affects the timing while the tps is at 0%. What I really want to know is will it make me faster in any way??