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Old 02-21-2011, 10:18 PM   #1
ricks71pu
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HEI * spark plug question

ok, here i go. i have a 1971 GMC 3500 (Longhorn?) with a transplanted 1975 454. It does have an HEI. Problem is, one head is an older 396 head. Each head has a different spark plug length! i am going to put NGK V-power plugs in, but will need to get 4 plugs with 1/2" threads and 4 plugs with 3/4" threads.by this i mean thread length. this does not bother me (too much). My question is, should i gap the 396 head with 3/4" length tread plugs @ .35, or @ .60? remember i have an HEI dizzy, and was told with this dizzy to gap plugs at .60. or should i gap at .35?
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Old 02-21-2011, 11:45 PM   #2
Wrenchbender Ret
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Re: HEI * spark plug question

.045 on all of them.
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Old 02-22-2011, 02:51 AM   #3
ItsRandy
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Re: HEI * spark plug question

You should put on a matched set of heads...just saying.
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Old 02-22-2011, 12:48 PM   #4
ricks71pu
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Re: HEI * spark plug question

yeah, matching heads is the right way. but were on motor when i bought truck. PO always used long reach plugs in both heads, and i did not notice difference till a day or so ago, when i went to change plugs.
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Old 02-22-2011, 05:44 PM   #5
MARKDTN
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Re: HEI * spark plug question

Quote:
Originally Posted by ItsRandy View Post
You should put on a matched set of heads...just saying.
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X2

It would bug me to death to have them mismatched.
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