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Thread: Outboard engine application

  1. #1
    jameskb2 Guest

    Default Outboard engine application


    I have a 1970 Johnson 3 cylinder 60 horse outboard engine that I am considering doing an ignition conversion on.

    I have found that the factory amplifier pack is a CDI box that is known for it's failure. This part is expensive, and since prone to failure, I figured I could upgrade.

    The MSD 6a box will work. It can use the point triggered system the unit has, and with little mods will bolt in.

    Here's the problem....

    Experience from others has shown that the hotter spark will blow up the stock rotor / distributor cap. Because of the tight quarters, ionized air removal is tough. The cap / rotor is out of production and is harder and harder to find, let alone expensive. Output of the factory system is 30k volts give or take, and there is no problem with that. Using the MSD system, 45k to 50k volts are produced, causing the problem.

    My question is, how can I reduce the voltage output to 250 to 300 volts to the coil? It's reported that using TWO coils with one coil's output grounded is working well. Basically one coil is used as a voltage sink so the final secondary output to distributor is 22k to 25k volts.

    I was hoping there was a setting or resistor I could install at the primary side of the coil to reduce the MSD 6a box output to 250 / 300 volts.



  2. #2


    You may want to look at the MSD5 box. The primary voltage is 375 volts. You still get 40,000 volts at the coil. Are you racing this engine?

    Thank you

  3. #3
    jameskb2 Guest



    I'll check that out. No, not a racing application. I just want to restore the engine to a solid performer.

    Stock and after market coils are 100:1 ratio. Could I use an alternate coil? Say one of your 85:1 or 70:1 units to reduce the voltage output? I'm actually shooting for a spark voltage of around 25k with 30k max.

    This is a point triggered system. 3 lobe cam triggering dual points (but I could reduce it to one set of points)

    Would a MSD 8230 coil (70:1) or the like work?

  4. #4
    loop Guest

    Default RPM capabilities

    How many RPMs would the MSD 5 box be good for in this application?
    I have the same motor but I would like to see 7500 rpm.

  5. #5

    Default 6a

    On a normally aspirated engine such as yours the MSD 5 or 6A should work fine. I would however recommend running our part number 8202 Blaster coil with this. The voltage numbers listed by us is the maximum efficiency of the ignition/coil under extreme conditions (normally racing applications). By this I mean any modifications you have done to your engine and or the addition of any component that will boost the performance of your engine such as a turbo or if you are running any type of exotic fuel. Being that your particular engine is stock it will not require as much energy(voltage) to jump the gap from the rotor to the terminals inside your cap or at the spark plug so that number could possibly be as low as 10-15 kv. The desired RPM of 7500 will not be a problem as well. Please let me know if you have any other questions. Thanks, Bret- MSD Powersports tech

  6. #6
    J-Jordan Guest


    I am also trying to do the same thing with a 6A on a stock 1969 Johnson outboard, just a fishing boat, max RPM of 5.5K, 130 PSI per cylinder cold. Noticed above that the lower output V from the MSD5 still gives the max coil output, is that correct? Is the 5520 the same as the "MSD5"? I am also concerned about burning out the dist/rotor. At what point would the estimated V be expected to rise above the ~25-30kV mark?
    Thanks Jack

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