HEI * spark plug question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ricks71pu · 02-21-2011, 10:18 PM

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?

02-21-2011, 10:18 PM	#1
ricks71pu Registered User Join Date: Feb 2010 Location: salem oregon Posts: 225	*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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