502 vs 427 heads

[fstblk66]

My 66 is currently having the motor totally rebuilt. I recently discovered that the heads (14097088) are GM over the counter BB open chamber 502 heads that have never been ported or modified in any way. All other parts in reference to the motor are all numbers matching L-72 427/425. My question is if I opt to install the correct closed chamber heads that originally came with the L-72 would there be any significant difference of power gain or loss. Thanks.

[Ken Anderson]

BIG gain!

[grumpyvette]

first ID point out that if your short block has the closed chamber pistons the swap will increase the effective compression ratio, back to well above 10:1 and Id suspect that the open chamber heads were installed to DROP the effective cpr below 9.7:1 so you could run the crummy gas we have now vs the 260 sunoco and similar leaded fuel available when that orignal engines much higher cpr was used.
if you have open chamber pistons the closed chamber heads have clearance issues
Id also point out that the open chamber heads have much less valve shrouding and tend to flow better, especially when minor bowl/port works done.
in theory just the cpr increase should yeild about 20hp
play with this and see what IM talking about

http://cochise.uia.net/pkelley2/crc.htm

youll (DEPENDS ON EXACT CASTING USED) be going from an open chamer near 115-122cc to a closed chamber between 98cc-107cc
if you have both casting numbers look here (below)

http://www.mortec.com/bbc.htm

[Kid_Again]

I can't add much to what was posted here. I would emphasize that unless you actually inspected the pistons, you have no idea what you have. So, do not swap heads without doing the math.

It seems that you're a # match kinda guy, which is fine. Other than that, why would you go back to the old closed chamber design?? Even if the flow numbers for the bare heads were the same (I am told that the old heads flow significantly less, not sure), I believe your heads have 2.19 intake valves and you have adjustable valve train components.

I have these heads on my zz440, I put roller rockers on them and am pretty darned pleased. Real decent for the street.