Spark Plug gap for MSD box

Discussion in 'Engine Topic' started by andymiller, Jul 30, 2006.

  1. andymiller

    andymiller Veteran Member Lifetime Gold Member

    Jan 30, 2006
    Anchorage, AK
    What spark plug gaps are you guys using with MSD boxes? I have a mild built 355 and running a MSD 6a box. Basically a stock type HEI dist. 9.6 cr
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    Nov 4, 2004
    Ringgold, GA
    I've been up and down the range of gaps and found .040 works best for me. Really, you'll just have to play around, but .040 will be a good starting point.
  3. Damon

    Damon Veteran Member

    Nov 16, 2000
    Philly area
    .045 is about where I run them. You can probably go wider but I never do on a street motor- the wider the gap the more strain it puts on the whole secondary side of the ignition. My brother runs them at .065 but he always seems to be replacing coils and coil wires a lot more than me. I usually go years without wearing out ignition components.
  4. Joekool

    Joekool Veteran Member

    Feb 4, 2002
    Hollister CA USA
    With 9.6 to 1 c/r .040 to .045 should be fine, if your compression where to increase then you would need to lower the plug gap. I have around 10.25 to 1 and .035 seems to work the best for my engine.
  5. andymiller

    andymiller Veteran Member Lifetime Gold Member

    Jan 30, 2006
    Anchorage, AK
    I've always heard you wanted tp run a large gap with these things to make a big hot spark.
  6. Marv D

    Marv D Veteran Member Lifetime Gold Member

    The larger the spark kernel the better, but when you start running more and more compression it is harder for the electricity to jump the gap, so you have to give up a large spark for reliability of the plug firing every time. At 14:1 you'll typically see the racing plugs gapped at around .028 -.32. But like Damon suggested, MSD suggests a starting point around .035-.045 for normal street compressions.
  7. blue 79 Z28

    blue 79 Z28 Veteran Member

    Jul 25, 2006
    Richmond b.c.
    i agree. for n/a i run .035 on mine, and for nitrous i run .030 thats with a digital 6 ignition, and just over 11:1 on the motor, never had a plug issue or ignition hiccup.

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