350 SBC head numbers don't match - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-14-2008, 05:21 PM
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350 SBC head numbers don't match

Oh boy.
I think I opened up a can of worms here, but this is my issue: I have a '34 Ford and was told it had a 350 bored .060, Corvette 2.02 heads, cam is 284 duration - 0.480 lift (that's all I know), 9:1 compression with Rochester 2G tri-power. The cam just seems too big for cruising, it idles like a dragster and bucks in first gear but runs great at 2500+ rpms. I replaced the ignition, rebuilt & adjusted the carbs, all else seems OK. It just seems to have a big cam. The plugs have a nice light brown color but the exhaust smells very rich.

So, I decided to pull the cam to see what it was and replace it with a milder one then as I checked the casting numbers on the heads...they don't match!

1) 3973487: '68-'72 350, 1.94/1.5 OR 2.02/1.6 & 75cc chamber

2) 3973493: '71-'72 400, 1.94/1.5 & 76cc chamber

I found several websites with info, but the bottom line is I don't know if my heads match or not. Worst case is one side is a 1.94 intake and the other is a 2.02?

Any advice is appreciated.
Thanks,
DB

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Old 03-14-2008, 06:22 PM
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Without knowing the history of the heads. It would be impossible to tell valve size from the outside. Neither head had factory 2.02 intake valves. Neither head is unlead gas compatible and will have seat problems with more than light use.

The reason for the poor performance and rich gas. Is probably the cam. A lot of those old ".480" cams were long duration, borderline stock convertor, bad idle quality, soggy bottom turds, if used in a basic stock engine/drivetrain situation.
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Old 03-15-2008, 11:36 AM
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Update after I removed the cam...

The Crane cam # is 10018, 286H06: Lift = 465, ADV duration = 286, Duration = 230/230.

Basic recommended RPM = 3200-6200 (rough idle) which is much too big for my cruising needs.

I'll leave these heads on for now and see how it performs after I decide on the right replacement cam (I'll research this board for cam recommendations, any cam tips for a 350 would be appreciated)

Thanks,
DB
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Old 03-16-2008, 08:15 PM
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F-BIRD'88, thanks for the great detailed info. I wish I was smart enough to make all of the required changes (or have you as a neighbor!). I'll go with plan B and install the smaller cam and keep the same heads (PS: they don't have push rod guide plates).

It's interesting the part about running the old cam timing at around 24 degrees initial. I thought something was wrong with my timing light or the degree tab on the timing cover. It just wouldn't run at 10-12 like every other SBC I had so I did run it around 24 and it made me nervous. Good call, at least I'm not too crazy.

http://www.hotrodders.com/gallery/sh...hp/photo/33578
http://www.hotrodders.com/gallery/sh.../cat/500/page/
DB
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Old 03-16-2008, 10:15 PM
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We had a similiar situation with mismatched bbc heads but they were 7 or 8 cc's off, could never tune that motor to run as it should. Doesn't sound like that is your problem but the standard issue 400 head has 194 intake and 160 exhaust valve which was unique to the big inch sb, not sure that would be the issue but worth noting.
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