I've read here that changing out the heads would be a big improvement to my '72 350. I found a pair of used 350 heads out of a '69 Cutlass. Would these heads give me higher compression and better performance?

 

They are suppose to breathe better ( number 5) but they will not have the hardened seats for modern fuels, it is not super expensive to have changed over and you can have the added benefit of installing larger valves etc. Not sure about the compression, I believe the 69s had smaller chamber ccs so that would increase the cr.

 

All the 350 heads have around the same combustion chamber volume (manufacturing tolerances will result in slightly different volumes) so swapping the 7A heads for 5 heads will not gain compression.

If your engine has the factory steel shim head gaskets and you replace them with commonly available aftermarket composition head gaskets, the compression ratio will actually go down due to the gasket thickness difference unless you compensate by milling the gasket surfaces. All this will net you the same compression as you started with, though.

One option is to have the 5 heads completely redone and milled for a smaller chamber volume. Be aware that at some point the intake mating surfaces will need to be milled as well so that they mate properly.

 

From what I've been reading, you've got good heads. But if you have anything over a 72 then you might get better compression with older heads 4,5,6,7,and 7a's all have around 60 to 64 cc's.
If you are interested in selling those heads though I am looking for a set. I have a 79 350 w/ 75cc heads. I would like to find some older ones.

 

No they don't, they're 68-70cc from the factory. Only the 330 4's wee down around 60cc.

 

http://www.442.com/oldsfaq/ofhed.htm

Bro, read up.

 

Thanks for the responses. I'm still not clear about this. One complication is that the motor was overhauled by the PO. I know the pistons were replaced, but don't know whether it was bored over. A cam--I believe a mild one--was installed; I have #15-16 vacuum at idle. Also an aluminum intake manifold and headers. That's all I know. The car runs good. Has the original q-jet carb, also "rebuilt." Never bogs. But since pulling the heads is relatively easy I would like to do that if that would improve performance.

 

It's been known for a long time that there is a lot of erroneous info on 442.com FAQ, Mark is right on the CC volumes that he posted.

 

Bro, it's wrong. How many have you had come across your bench that you've actually checked? I'm going to guess 0.

 

Thank you btw.

 

You're right. I haven't checked but thats not the only site that quotes those numbers. If you don't mind post your numbers that you've checked. I would love to have true numbers.

 

Frome Joe Padavano talking about my 79 350 heads "Unfortunately those heads have 75cc chambers and very low CR. An easy upgrade is to use the early heads from a 1967-1972 motor with casting numbers 4, 5, 6, 7, or 7A. Any of these will have chambers about 64cc or so." seems to be very well studied in olds motors.

 

I've had a half dozen run across my bench. Every one was in the 68-69cc range.

 

I conducted a poll on RealOldsPower several years ago asking those who had actually measured the chambers on original 5, 6, 7, and 7A heads to post up the measurements. Most reported 66-70 cc, with a very few (maybe 2?) 64-65 cc measurements. Seems as if those were the oddballs and ~68cc was typical.

 

What size are the chambers on the late model 350's? 75 to 79?