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Old 03-26-2011, 08:32 PM
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chevy heads (3991492) ANY GOOD?

I just got a old 350 chevy motor with casting number (3900010). The heads are (3991492)

I wanna stick them on my 84 (305) chevy motor. Good Idea? The heads have the small little humps on the front with acc. holes.

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Old 03-26-2011, 08:36 PM
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there good! 202 intake 64cc heads but you will run into valve cyl wall interference with them on a 305.

and if you do manage to clear up the interference problem performance would suffer due to poor air flow between the valve and cyl/deck
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Old 03-26-2011, 08:38 PM
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Also not compatible with unlead gas.
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Old 03-26-2011, 10:40 PM
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Better idea would to be rebuild the old 350 and ditch the 305
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Old 03-27-2011, 11:16 PM
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thanks

what would happen if you ran em' with reg gas
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Old 03-28-2011, 07:59 AM
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lead was used as a lubricant in older cyl head on the valve seats.

all you need to do is take them to a machine shop and have hardened valve seats put in average cost $200

then your good for unleaded fuel
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Old 03-28-2011, 08:30 AM
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ok

thanks
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Old 03-28-2011, 08:38 AM
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Quote:
Originally Posted by mud bros
lead was used as a lubricant in older cyl head on the valve seats.

all you need to do is take them to a machine shop and have hardened valve seats put in average cost $200

then your good for unleaded fuel
They're 64cc heads, so you'll need to heavily angle mill them to get decent compression, probably around .150" or so. If the seats are not too far sunk already you can get by without hardened inserts, but not with much spring pressure.

IMO you're better off going with a good set of used aftermarket heads, the 492's typically have excessive guide wear and if you need seats, a valve job, angle milling, etc. you're looking at $500+ in machine work in most cases.
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Old 03-28-2011, 05:10 PM
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Check intake valve to block clearance on a 305 bore.
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Old 03-28-2011, 05:22 PM
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Quote:
Originally Posted by ap72
They're 64cc heads, so you'll need to heavily angle mill them to get decent compression, probably around .150" or so. If the seats are not too far sunk already you can get by without hardened inserts, but not with much spring pressure.

IMO you're better off going with a good set of used aftermarket heads, the 492's typically have excessive guide wear and if you need seats, a valve job, angle milling, etc. you're looking at $500+ in machine work in most cases.

i cant think of any small chev head with less than 58cc chambers going to 64cc would barely make a difference 9.4:1 would change to 9.0:1 not enough to justify machine work
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Old 03-28-2011, 07:43 PM
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Quote:
Originally Posted by mud bros
i cant think of any small chev head with less than 58cc chambers going to 64cc would barely make a difference 9.4:1 would change to 9.0:1 not enough to justify machine work
Find a compression ratio calculator you like online and start using it.

On the small bore 305, going from a 58cc head at 9.4-1 compression to a 64cc head results in the compression ratio dropping to 8.7-1. Thats a pretty big hit.
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Old 03-28-2011, 08:38 PM
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i took a shot in the dark as there is a ton of info missing to use a calculator correctly.

i thought that would be close enough not to get flamed
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