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Discussion Starter · #1 ·
I have a 4.2 with the GM HEI dist. Getting ready to change the plugs. Per Performance dist they recommend .50 to .55, but I've seen some messages lately that suggest others may go up to .60. Even noted a improvement from .55 to .57.

Any feedback?
 

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I gapped mine at .045 and they seem to be burning just fine. /ubbthreads/images/graemlins/grin.gif
 

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Discussion Starter · #4 ·
With the high output of a HEI distributor, i've always been told to open up the gap and take advantage of the juice that HEI offers. To your point .045 maybe does get the job done for the most part.
 
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That is what I used. I doubt you will see a difference between .045 and .060. It usally only makes a big difference with higher compression and RPM's.....not exactly something we do with the 4.2.
 

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HEI will jump .060 fine --- BUT -

You should use the stock plugs originally designed for the head. If you widen a plug that was designed for .035 (stock) to .060, the ground electrode will be deformed - the spark won't jump correctly. It wants to jump from a sharp edge to a sharp edge. That far open it'll jump to the middle of the ground electrode, not the tip's edge.

The plug needs to match the head, not the source of the spark. Don't use plugs designed for the HEI in another engine.
Don't use aftermarket or "gimmick" trash, no plats, splits, multi's, colorful or other junk. They are designed to sell, not to use.

Use the stock original plug - then you'll have the right heat characteristics, indexing, and position.

Sooo - best way - open them up to .045 - replace when they get to .050.

Going from .035 to .045 makes a nice difference in idle, but still lets it rev higher than you want to go.
 

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Ran 0.45 in mine when it was in. Played with it up to .60 myself and like Rich said it killed plugs and wires for me.
No tech crap but just what worked for me.
 
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