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Thread: Is it possible to convert a HEI EFI Large Cap Distributor....

  1. #1
    Carb and Points!
    Join Date
    Jul 2016
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    2

    Is it possible to convert a HEI EFI Large Cap Distributor....

    Hey guys doing some research on ignition systems after finding my DUI Distributor coil and ignition pickup went out on a new distributor with less than 500 miles on it. Hear it is common with most internal distributor coils from heat. Most solutions come from switching over to the newer Corvette style small cap distributors with external coils, but here the external coils can go out just as easy. Although I could gain some clearance for upgraded -8AN gas feed and return lines coming from the end of my TPIS fuel rails and cramped distributor into firewall clearances.

    Emailed Dave Ray for his feedback on small cap distributors, he claims to just use the stock GM Distributor and then he drills out the distributor gear recess to accept the .491 dia. oil pump shafts, then he uses a stock oil filled coil that dissipates the coil heat much better for longevity. He claims to only use a max of .045 plug gap though.

    https://www.summitracing.com/parts/aaz-84-1830

    https://www.napaonline.com/en/p/ECHIC12

    https://www.amazon.com/Chevy-Distrib.../dp/B075QLHMPQ

    You can get the small cap conversion harness off Amazon for easy connection. Although I see possible pricey distributors MSD #8366 for $350 with .500 dia shaft and ball bearings that may not need distributor gear modifications, unless you want a bronze gear.

    Then, I got side tracked with the notion of wiring in a MSD 6Al ignition box for multiple sparks below 3000rpm @ 540 volts with spark plug gaps set to .05 - .06 and found a HEI ignition pickup bypass harness that they take from the 7-pin ignition module on the Large Cap distributors, using the external MSD coil adapter in place of the internal coil on top of the distributor cap.

    https://documents.holley.com/8875.pdf

    https://www.holley.com/products/elec...ses/parts/8861

    http://www.gearhead-efi.com/Fuel-Inj...8-MSD-Ignition

    https://www.holley.com/products/igni.../parts/8401MSD

    Both setups would work with the MSD 6A ignition box, although I could utilize the new DUI distributor body to gain multiple spark at lower rpm's and even leave the internal coil for now - still having spark advance coming from the EBL ECM.

    Has anyone done either conversions using the MSD 6Al ignition boxes on the HEI/EFI distributors of Large or Small cap style?
    Pros and Cons?

    Only thing I have found is caps, rotor and spark plug wear increases - Da! But for rich AFR, higher lift cams, etc you gain better fuel efficiency with multiple sparks on the street.
    Last edited by heinzeroth; 1 Week Ago at 07:44 AM.

  2. #2
    Carb and Points!
    Join Date
    Jul 2016
    Posts
    2
    Talked with Holley/MSD support rep and he says any 6-series ignition box will work to enhance coil voltage to 540v with a multiple of 3 sparks within 20 deg at firing per cylinder and all instructions and wiring comes in kit - NOT needing the #8875 harness, but looks to be much easier connection and more stable over time without creating a big tape ball with electrical tape to hold everything together. Think I'm going to order the MSD 6A ignition box and give it a whirl!

    MSD Instructions

    Note: Instructions says not to use digital timing lights on tuning motor!
    Last edited by heinzeroth; 1 Week Ago at 07:47 AM.

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