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Old 03-20-2004, 02:44 AM
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porting 3917215 chevy bb head

Hi guys

I've reading up on porting heads in here and on the web, and i think i'll try to port my 3917215 bb heads. I was thinking of port matching the intake head, remove the casting flaws, bowl blending them, and polishing the exhaust ports...

Does this sound okay and are there any special consideration with the the 3917215 chevy bb head I need to be aware of?

Sune

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Old 03-20-2004, 07:07 AM
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These are early heads with the "N" series spark plugs. Small bathtub chamber. These were notorious for guide and valve stem wear. Check for wear and correct. Guide wear is a leading factor for dropped valves in big blocks, keep them snug. To be correct for modern fuel you will have to have hard exhaust seats installed. If you do, have seats for 1.88 exhaust installed and use aftermkt stainless valves. These heads are a bit restricted on breathing on the intake side because of the combustion chamber wall. Anything you do to relieve the wall around the intake(taper chamber into head face surface) will help, If you can handle a little compression ratio loss. I usually bowl hog the intakes and install 2.19 intakes. This will help breathing too about 5500-6000 rpm.
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Old 03-20-2004, 09:25 AM
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Quote:
Originally posted by BOBCRMAN@aol.com
These are early heads with the "N" series spark plugs. Small bathtub chamber. These were notorious for guide and valve stem wear. Check for wear and correct. Guide wear is a leading factor for dropped valves in big blocks, keep them snug. To be correct for modern fuel you will have to have hard exhaust seats installed. If you do, have seats for 1.88 exhaust installed and use aftermkt stainless valves. These heads are a bit restricted on breathing on the intake side because of the combustion chamber wall. Anything you do to relieve the wall around the intake(taper chamber into head face surface) will help, If you can handle a little compression ratio loss. I usually bowl hog the intakes and install 2.19 intakes. This will help breathing too about 5500-6000 rpm.
Thanks for your reply.

I'll be running 95 octane leaded that way I would be able to run them without changing the seats... right?

btw. how do I check for guide wear?

Sune
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Old 03-20-2004, 10:39 AM
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First clean your valves good in a degreaser, on the valve stem about 5/8-3/4" down from the retainer end, visually check for wear thru the chrome plating. If you can't see it take the valve stem between your finger tips and run the stem up and down, you will feel any wear. If you can feel it, the stem is junk. To check the guide, install a new or unworn valve in the cleaned, dry guide, all the way in, then pull it out about 1/2" and try to move it sideways and back and forth to the side. If you can feel any motion, you will need guides. the clearance is only .001-.004" on a cast guide, at about .003 jou can just barely start to feel the side motion.
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Old 03-21-2004, 02:11 AM
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hi bob.

thank you i'll try that.

Sune
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