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I have just installed in my 65 with a 289 a PerTronix 40,000 volt coil and 8 mm Flame Thrower Wires. Suggestions as to what would be the proper spark plug gap for this set up. Also any input as to if i should replace the resistor wire with another wire or not? I have gotten different advice on this, both saying yes and no.
 
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With the flamethrower coil, Pertronix says you can run them even up to .050. Mine are set at .042 and seems to work well.
 

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I think Pertronix is a bit optimistic with the .050" gap... I find .040" to .045" is optimal!
 

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The whole reason for wide spark plug gaps was to have a longer burn-time with lean fuel mixtures so all of the fuel mixture would be burned. Carbon molecules are farther apart in a lean fuel mixture and with a weaker coil the spark tends to die out causing a lean misfire. So starting in the 70s cars started having a higher coil output with wider spark plug gaps with leaner carbs to prevent lean midfires which would result in higher hydrocarbons.

So with a car like yours a wider gap really isn't needed. A gap .040 is probably a good place to start.
 

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With the Pertronix FlameThrower coil, Pertronix wires, and Pertronix Ignitor in my son's car, we ran a gap of .040. The plugs would last about 2k miles and then were toast. Tried it twice before setting them back to the stock .036 and never had another problem.

Now if you're running an MSD6A type box, I think it's different. With an MSD billet distributor, MSD 8mm wires, Blaster II coil, and MSD6A-L, I run a gap on my '66 of .051

Personally, I couldn't tell any difference at all in running the .036 and .040 in my son's car, other than the plugs would last longer.
 
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Have not instaled the Pertronix Igintor yet but did gap my plugs at .42 mm , car ran like a bat out of hell, will check what they look like as per your experance in 2k to see what they look like. Drove the car around the farm once, it's a thousand acres, and no i don't own it, and had the drive lights cut out on me coming home for a couple of seconds, first time that ever happened! have not replaced the resistor wire, could it be related?
 
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