cc size cylinder heads

cc ed my heads and they are 56 cc. whats the rule for milling heads? if i mill the heads .020 what does it reduce the cc to?

 

Don't guess.
If your heads are open chambered, measure the circle and do some math.

 

i could, just figured this was a very common procedure that someone would know.

 

That's a good idea.

I just measured my '71 heads and the average dia is 3.765", so .020" off of those would be about 3.649cc
my '74 head averaged 3.780" dia, so .020" off those would be about 3.644cc

 

I mill a lot of heads and don't guess or use tribal knowledge.
It's easy to plan what you want it to be.
Bore squared x .7854 x depth (.020") ...then convert to cc (x 16.39) [for round open chambered heads].
Takes less time than either of us to have typed our responses.
Brackets and parentheses not inferred for math purposes.
Wait for the fish to commit to the bait before you set the hook......oh, you know what I mean


All meant in good humor!

 

thanks, just playing with the compression calculator on summits website. is removing .025 from the deck safe?

 

I had my block decked .050 all was good.
My iron heads were milled .030 all was good.

 

Structurally speaking, .025" is usually nothing to be concerned about.
The surface you are looking at would have to already be pretty thin.
With every head, you need to look it over to ensure it wouldn't be drastically changing the sealing surfaces or altering the water transfer passages.
A chip on the edge of the casting or a chamber that might move itself off the gasket could be an anomaly to any casting itself.
Normally, a concern for a minor amount of milling is for valvetrain issues where there isn't adjustability.

 

Guesstimate around 4 or 5 cc for .020 off head. But they all vary slightly. Would need to measure afterwards to confirm. You might want to check valve clearance to confirm that’s good afterwards

 

With the average diameter of 3.775" and a .020" cut, I get 3.67 cc (rounded), not 4-5.
.3 to 1.3 cc doesn't mean much in the grand scheme of things, but a bigger depth of cut and several things guessed as some kind of rule and tolerances stacked up with errors ...would lead to being misinformed. js.