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Extender resistance with Black Stallion electronic ignition

Discussion in '308/328' started by GT4andMore, Jan 13, 2021.

  1. GT4andMore

    GT4andMore Rookie

    Oct 23, 2020
    15
    Full Name:
    Graham
    #1 GT4andMore, Jan 13, 2021
    Gents,
    Another after-market modification on the new GT4 is an electronic ignition system from Black Stallion Motors (BSM) in Australia. This looks like a nice unit and the car fires up and revs eagerly so I am optimistic this is a good system to have on board. HOWEVER....

    ... at least one of my spark plug extenders is cracked with a piece missing so I ordered a complete set from Superperformance in the UK.

    The old/broken extender has a resistance of 375K ohms. The new extenders have zero resistance. The plugs are Bosch W7DTC also zero resistance.

    I have read endless posts on this forum and elsewhere that state/imply that transistor based ignitions, which I assume includes BSM, need some resistance in the ignition circuit. My instinct therefore is to swap the zero resistance extenders for some with resistance. Whatever happens I don't want to damage the BSM unit as it comes with a non-standard distributor so ending up replacing the entire ignition system for the sake of a $10 extender would be a total disaster.

    Are there any other BSM owners out there who could advise on their extender/plug combination and whether 375K ohms paired with a Bosch W7DTC is in anyway optimal.

    Thanks as always for a great forum.

    Graham

    (BTW the wheels in my last post are still on the car awaiting the renovation/upgrade of the electrics)
     

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  2. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,388
    Along the Verde , AZ
    Full Name:
    Doug
    #2 AZDoug, Jan 13, 2021
    375K ohms is way excessive on any ign system. Carbon core wires have about 1000 ohms/inch resistance, for comparison, a 36" wire is 36K oms

    I have use breakerless electronic ign systems for decades with solid core plug wires and non-resisting spark plugs. Resister plugs is for ~1970s emission control vehicles.

    I have the BSM in my 308 and use the wires they supplied and factory extenders and non-resistor plugs. I never measured the resistance of the extenders, but assumed they were/are about zero. You have whole bunch of resistance built into the airgap on each spark plug.

    Doug
     
  3. GordonC

    GordonC F1 Rookie
    Rossa Subscribed Owner

    Aug 28, 2005
    3,779
    Calgary, AB, Canada
    Full Name:
    Gordon
    #3 GordonC, Jan 13, 2021
    If you want to change one element, go with the zero resistance extenders and switch to resistor plugs - the NGK BPR7EIX is a popular choice for high energy ignition systems, there are many recommendations here for it with stock Digiplex ignition systems on i and QV cars, as well as with aftermarket ignitions like the Electromotive XDi.
     
  4. GT4andMore

    GT4andMore Rookie

    Oct 23, 2020
    15
    Full Name:
    Graham
    #4 GT4andMore, Jan 14, 2021 at 10:38 AM
    Fantastic - thanks both. I was planning to replace the plugs anyway so have ordered a set of NGK BPR7EIX and will retain the new, zero resistance, extenders. I will report back once everything is installed. Hopefully it will be a short post!
     

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