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Old 12-26-2007, 08:40 PM   #1
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head numbers

i found these heads the vavles look unusually large. i have checked online at the casting numbers but cannot find anything on them i was hoping that someone could let me know about these heads.

the numbers are
3888338 on both heads
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Old 12-26-2007, 09:04 PM   #2
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Re: head numbers

take a closer look at the casting number. more than likely its 3986336

early 70's 76cc smogger. Was used on 1971 1972 350 LT1 Z/28 (330hp and 255net hp) so could have 2.02 x 1.60" valves with guide plates.
One of the better large chambered smoggers. Not too bad with full on porting.
Kind of old stuff. Not worth paying $$$s for. Lots of better heads today to choose from.
Not bad (with lots of porting) when building a low compression supercharged 350 on a strict budget.
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Old 12-26-2007, 10:01 PM   #3
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Re: head numbers

i will take a closer look.

i am building a 400 with je pistons the site said that the pistons are 11:1 with 76cc heads. so i am ok with bigger chambers.

so i got the heads for free are they worth putting the money into the porting or is it better just to get a different set of heads to start with?
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Old 12-27-2007, 09:17 AM   #4
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Re: head numbers

the early 70's SBC heads are ok....they have hardened exhaust seats for unleaded gas. BUT, they have very small intake runners by todays standards. if you are going to port these by yourself then go, but if your taking these to a shop to open up and flow, then dont waste your money, grab a set of aftermarkets, because professional porting isnt cheap, and these old iron heads only go so far. Up here in canada we have 94 octane gas, but i beleive in the US its as high as 91....so for 11:1 compression you are going to need to run a mix of 91 and race gas....probobly 50/50 to obtain a 100 octane so you wont detonate. I would steer towards an all aluminum head, that way you are able to run 1 more compression point compared to iron. so 11:1 will act more like 10:1 with the aluminum head and you would be able to run 91 octane with a bottle of octane boost to help with detonation.
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Old 12-27-2007, 04:10 PM   #5
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Re: head numbers

i did recheck the numbers and i am sure they are 338
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Old 12-27-2007, 04:20 PM   #6
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Re: head numbers

Probably not.

Here's the numbers close to that.

3986336....71......350..........76cc chamber
3986336X...71......350..........76cc chamber
3986339....71......307/350......74cc chamber
3986339X...71......307/350......74cc chamber
3986388....68-76...307/350

Probably one of those.

None of them are particularly good. Some of them are sort of OK for a 350, except for the ones that also came on 307s (2-bbl heads); but even the best stock heads would be thoroughly unsuitable in this day and time for a 400 with dome pistons.

I would not put my money into them.
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Old 12-27-2007, 04:30 PM   #7
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Re: head numbers

thank for all of you answers I do appreciate it. I am going with aftermarket heads.
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Old 12-27-2007, 04:54 PM   #8
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Re: head numbers

Do the JE pistons have a dome on the top? If so send them back for ones with a 18-22cc dish (64cc head) or flat top 72-76cc head, or your motor will have excessive compression ratio for pump gas.
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Old 12-27-2007, 06:39 PM   #9
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Re: head numbers

Check out the MorTec website. Chances are they have your heads listed.
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Old 12-27-2007, 06:39 PM
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