Spark plug gap on 347 stroker with gt40x heads? - Mustang Evolution

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Old 12-11-2011, 02:45 PM   #1
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Spark plug gap on 347 stroker with gt40x heads?

Hi, i recently bought a 1988 mustang gt with a fuel injected 347. It has gt 40x heads with the gt40 upper and lower intake, full exhaust, 70mm tb, cai,76mm maf, no air, electric fan, no smog pump, has cam and rough idle(dont know cam size),24# injectors, aluminum drive shaft, 3.55 rear, beefed up t-5, etc. It has msd ignition with multispark but the distributor is motorcraft for some reason. It currently has autolite 3923s in it with a gap of .045 and the timing is 10 tdc with 22 total. This combo has me wondering what gap i should be at for optimum power without spark plug blow out. I was told to change the plugs to the motorcraft AGSF-32M or autolite 104s cause the heat range was too cold. Need help and dont know much more about the motor and cant reach the guy who built it originally. i know the heads are not the greatest and would prefer some trickflow or afr 185s but would like to work with what i got for now.
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Old 12-11-2011, 02:46 PM   #2
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Spark plug gap on 347 stroker with gt40x heads?

.044 - .045 is about right anytime you have electronic ignition in a Ford, GM or Chrysler.
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Old 12-11-2011, 03:28 PM   #3
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Spark plug gap on 347 stroker with gt40x heads?

the only thing that is going to matter in terms of spark plug gap is what ignition you have. I read the other answer 35 th is too small a gap, that is ok for a ignition with a points set up, but an msd ignition is going to completel fry the electrodes right out of the plugs. 45 th is what most electronic ignitions would be set at, but call any auto parts store and ask them. they can look it up,
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Old 12-11-2011, 04:26 PM   #4
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Spark plug gap on 347 stroker with gt40x heads?

Auto lite 3923 and 104 is not even the same plug design.

3923 is a 14mm thread, .750" reach, 5/8" hex, tapered seat plug
104 is a 14mm thread, .708" reach, 5/8" hex, tapered seat plug
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Old 12-11-2011, 04:55 PM   #5
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Spark plug gap on 347 stroker with gt40x heads?

i would set plugs at .035
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