I have a couple of 350 blocks and heads and was looking for the most cost effective way on a rebuild to increase compression to around 9.5:1.

The heads I have are cast 47 (2 sets small valves and 72 cc) and a set of 4X-3H (large valves 98cc).

I could deck the block but that will only gain me about 0.5 on the compression ratio.

I have built many chevy engines and just picked the piston with proper dome to get desired compression ration however it appears Pontiac only has flat tops and with good flowing heads, the CR is too low.

My preference is to build a Pontiac but if the costs are too high I will need to consider a SBC.
What have you guys done and what do you recommend?
Thanks,
Tom

Not a lot of options on the 350.
You can zero deck the block, mill the heads a little, which might get you to where you want to be. There's only one stock piston available anymore the 350, otherwise you could go with a custom piston that would raise your CR. (There was an article a while back in one of the magazines on how to modify a small block Mopar piston for use in the Pontiac engines, if want to go that route.) Or spend a lot money on aluminum heads.

I would CC the 47's to see where they are at

I have seen a few 65cc alum heads lately for sale on PY. Not sure what that will give you but will probably get you closer if you wanted to spend that kind of money. Kind of a waste of effort on a 350.

I believe #16,#48,#62 heads all have 72 cc chambers and should give you approx. 9.2 cr. they all have 2.11 intakes and 1.77 exhausts. According to SD performance you don't want quite as much compression in a pump gas pontiac engine as you could get away with in a small block. Like Mushroombert says you can go to a zero deck height, increase your cr a little and get a more efficient burn and come closer to the compression your looking for. Add .5 compression ratio if you go to aluminum heads to achieve the same results. I've seen these heads selling on CL and KIJJIJI for $50- $200. SD performance sels them complete CNC ported to 240cfm, springs etc of your choice for $1500. Read Jim Hands book "Max Performance Pontiac V8s". Lots on efficient horsepower. Once you go pontiac you won't go back.

Neill, next time you see alum heads for a Pont for $200 you let me know. Cheapest I've ever seen has been $1000 for some that needed work.

What would be the psi of 9.5:1 in a pontiac 350?

Ha! sorry Robert, I made that sound confusing. I meant the cast heads for that price.
The psi of that engine depends on camshaft selection, please read Jim Hands book and study static and dynamic compression ratios. good luck

Always CC you heads to be sure. those numbers vary head to head and casting to casting.
My #16's were 77 cc and that was after a clean up mill to the deck surface.

Not sure where in il you are but I have a few sets of heads, sold the 16' s but I have #13, might let a set of #62's go, I have a 71 400 with 96's might have a 69 400 with 16's coming in sometim in feb not sure but if it is date correct for my bird may keep it if not ill sell it, supposedly out of a 69 bird,
Let me know if you are interested in anything

there is a good article on this site in "hall of fame" on compression ratio

You will increase compression by about .2 for every .010 you remove from the deck height. You will also increase compression by for around every .025 you remove from the head. Every .025 off the head reduces chamber size by around 4-5 cc's. See the chart below. Here's a quick wallace racing comp calculation. You may have to mill the intake slightly if you take .025 or more off the heads.

350 bored .030 over.
head gskt id 3.925
Piston belowdeck by .020
72 cc heads milled .025 to 67 cc.
Compression = 9.59
Compression with 72 cc = 9.12

Hope this helps




Head milling chart

http://wallaceracing.com/headmill.htm