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Thread: Experiments with increasing idle timing on B28F

  1. #1
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

    Posts:    1,148

    My VIN:    10270

    Experiments with increasing idle timing on B28F

    I recently ran some experiments changing timing in the idle zone. 13 degrees always struck me as late given that a stock distributor averages 30-40deg during cruise loads.

    I found that 19 degrees BTDC saw a measurable decrease in MAP and measurably reduced injector PW. Idle feels less lumpy, and transitioning from cruise back to idle shows less tendency to rev hang. Idle advance correction seems to have more affect at this higher range.

    Just wondering if anyone with ignition control + idle advance correction has tried something similar?
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  2. #2
    Senior Member
    Join Date:  May 2011

    Location:  Northern NJ

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    My VIN:    10757 1st place Concourse 1998

    Base timing for an older mechanical system has to be set to meet a bunch of compromises. They include;
    Ease of cranking and starting
    Emissions
    The octane of the fuel to be consumed
    The operating temperature of the motor
    Acceleration and mileage

    You can only do so much with a mechanical system. An electronic management system can do a lot more and is easily adjustable. You can optimize every parameter at all points of the operating envelope. The mechanical and vacuum advance can't be adjusted nearly as well as you can with an electronic system.
    David Teitelbaum

  3. #3
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

    Posts:    1,148

    My VIN:    10270

    So far 19deg is amazing. I have cranking at 10deg and the immediate transition to 19deg gives a satisfying startup "flare".

    Idle is more stable. Engine feels smoother. Off-throttle transitions are smoother. Idle advance control has a lot more affect with base timing at 19 vs 13. Seems like 13 is so late that removing any more advance doesn't have a lot of affect on actual RPM.

    Anyone with an odd-fire + ignition control should give it a shot.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

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