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Old 04-22-2012, 12:00 PM   #1
dmaclaren
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Default 69 351 w spark plug gap .032-6 or .042-6

I have read both and in pulling all my plugs, they are in the .042 - 6 range.

Are my gaps off from the previous owner or is that right? it's a 1969 351w
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Old 04-22-2012, 02:55 PM   #2
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the shop set mine at .030" lots of people run .035".

the bigger the gap, the higher the voltage, which i would expect to be harder on wires/caps/rotors.
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Old 04-22-2012, 04:41 PM   #3
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I'm running electronic ignition, I have them gaped at .046, wonder if I should reduce to the .036. I was just reading that for elec. ign., .04x is the way to go.

Now I am not sure
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Old 04-22-2012, 04:49 PM   #4
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there seems to be a love affair with increasing the gap with a more powerful ignition system. i personally don't understand the rationale. maybe someone here will explain it to me.
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Old 04-22-2012, 10:22 PM   #5
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I run .045 with an electronic ignition and .036 with points. The bigger gap allows for a bigger fatter spark. An electronic ignition has more volts to jump the larger gap.
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Old 04-22-2012, 10:43 PM   #6
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I have mine at 40, NGK plugs with MSD 6AL box. I don't notice a difference, I was told between 35 and 45, so I set it at 40. A bigger spark makes for a more complete burn I guess?
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Old 04-23-2012, 12:30 AM   #7
Starfury
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It helps ignite the mix more reliably. GM HEI systems (which use ~100kV coils) are commonly run with a .050-.060" gap.

With a stock coil and electronic ignition, I'd say .035". With an aftermarket 40kV coil, call it .040.-.045".
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Old 04-23-2012, 12:30 AM
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04, 1969, 351, 8mm, cobra, gap, gapping, ignition, msd, mustang, oem, plug, plugs, proper, size, spark, windsor, wires

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