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Thread: Should a Timing Map Be Linear or Expoential?

  1. #1
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    Default Should a Timing Map Be Linear or Expoential?

    When comparing the 3D shape of the factory timing map's shape I noticed that it appeared to be more exponential than my most recent map (at least the areas I addressed). My previous map was focused more on smaller RPM and load regions (high load/lowish RPM representing me dragging a trailer and holding OD) whereas my most recent iteration is theoretically more ideal across a broader range based on datalogs where I capture brief periods of substantial knock activity. Only a road test and datalogging will tell where I went right and wrong, but I am wondering mostly with respect to load increase/decrease is the engine's desire more linear or exponential and perhaps where is that threshold? It seems the areas I was closest to correct according to the knock sensor were areas where I was closer to the optimal timing, but clearly there were areas where both me and the tune were lazy so I had to combine the 2 to get what I believe in this moment is superior to what I currently have. For shits and grins here's the before and after. Truck's mods are as follows:

    98 Sierra L31 350 Vortec with Marine cam, 1.6:1 Comp Pro Magnum roller rockers, 1 5/8" long tube headers, dual 2 1/2" to single 3" exhaust with Magnaflow muffler, unknown underdrive pulley, and these tunes:

    And for some gay ass reason I can't add my newest tune to the list? POS won't upload without a red X?
    Attached Files Attached Files
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  2. #2
    EFILive Distributor dfe1's Avatar
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    Default

    If I understand you question properly, ideal timing is neither linear nor exponential. It seems to be linear to a point, and then it flattens out.If you look at most timing maps, they increase linearly to approximately peak torque, then flatten or tail off. Combustion chamber design also has an influence on the slope of the timing curve. Typically, LS engines like less aggressive timing than traditional small blocks.
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