Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI - Chevelle Tech
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post #1 of 10 (permalink) Old Sep 2nd, 08, 2:16 AM Thread Starter
Steve
 
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Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

What should the gap be? AC Delco brand new plugs. Going to gap them, but don't know to what. Asked around, I have heard things from .035 to .054. Brand new out of box. I doubt it should be at .054. I was thinking around .042 or something around there.

Haven't done this before, and I know someone on here has. Any info would be appreciated. Thanks all.

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post #2 of 10 (permalink) Old Sep 2nd, 08, 2:32 AM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

You're correct about .0054 being too large. You were close, but most folks including myself gap plugs with an HEI at .0045

You'll be really happy with the upgrade!
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post #3 of 10 (permalink) Old Sep 2nd, 08, 2:43 AM Thread Starter
Steve
 
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

Awesome thanks! I asked on Yahoo! Answers and I have heard all those. But I will stick with what you said and see what happens. Should work out well. Thanks a lot!
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post #4 of 10 (permalink) Old Sep 2nd, 08, 8:06 AM
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Smile Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

Stock points was .035 so .045 is a good place to be with hei as already suggested.

scott

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post #5 of 10 (permalink) Old Sep 2nd, 08, 8:56 AM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

I was just curious, but what if you had the gap at say .035 for HEI? Does it not burn the fuel as efficiently?

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post #6 of 10 (permalink) Old Sep 2nd, 08, 12:04 PM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

I own an early Safari Van with 4.3 V6 and stock HEI, and that specification IS .035. But, with every other HEI I have, the gap is set to .045. The key is, if the compression ratio goes up, drop the gap down.

GM made a real mistake with HEI performance during their Oldsmobile years, they specified a spark plug gap of .060, and even later, .080. This was done to make sure the molecules of fuel could bet in between the plug gap, to get lit off, because the mixtures were so lean, those fuel molecules got further apart from the leanness. The gap had to be giant in order to get enough fuel molecules into it, to get the light off done. GM found that the giant gaps were killing many, many electronic components, namely coils and modules. So, the lesson learned is, stock compression ratios, .045, higher performance comp ratios, drop the gap, and don't gap your plugs larger than .045, no matter the coil, module, etc.

Regards,

Milton
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post #7 of 10 (permalink) Old Sep 2nd, 08, 3:11 PM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

WHAT PLUGS?

Plugs designed for a .035 gap often won't be too thrilled about being opened to .045.

If you bought stock plugs, use stock gap.

If you bought plugs for a newer vehicle with HEI, use the HEI gap. (preferably around .040--.045.) The ground electrode is longer, allowing the bigger gap.

Yes, you can buy plugs designed for a huge gap; you don't want those.
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post #8 of 10 (permalink) Old Sep 3rd, 08, 3:31 PM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

Sorry for the hijack but I have a 1970 chevelle with a HEI and the Accel header plugs gapped to a .035 and was thinking about raaising the gap to a .045 but wasn't sure, and from what I read this would make a difference correct?

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post #9 of 10 (permalink) Old Sep 3rd, 08, 4:31 PM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

I'm using AC rapidfire #1, gapped at 0.045. I think the heat range SHOULD be a #2, but I had them, so I just put them in.

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post #10 of 10 (permalink) Old Sep 3rd, 08, 4:41 PM
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Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI

I've never had problems with negative electrodes when opening/closing the gap properly.

The only plugs I wouldn't re-gap are the ones preset for a specific gap, like the NGK's with the suffixes 9, .036, and 11, .044.

Regards,

Milton
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