combustion chamber volume

[Bobby Zlatkin]

sbc 76cc head.

Approx. how much needs to be removed from the deck surface to reduce the chamber volume 1cc? I know it's not an exact ratio as when you get deeper into the chamber you have to cut more to remove a cc. Just looking for a general rule of thumb.

Trips back & forth to the machine shop are both costly and labor intensive.

Thanks

[rawhide]

Originally Posted by Bobby Zlatkin

sbc 76cc head.

Approx. how much needs to be removed from the deck surface to reduce the chamber volume 1cc? I know it's not an exact ratio as when you get deeper into the chamber you have to cut more to remove a cc. Just looking for a general rule of thumb.

Trips back & forth to the machine shop are both costly and labor intensive.

Thanks

Bobby,
It is difficult to pin down an exact figure but I have found it usually takes .006"-008" to remove 1 cc when the head is virgin. I realize that the word virgin is never used around the drag strip but I am using it anyway.
thanks, Roland

[Greg Reimer 7376]

On the '68 3917290 327 head, the spec called for 68.9cc's, the OEM head was actually around 79 cc's, I found that it took around .008" per CC desired to get these heads down. I think it was around .078" to get it real close. It took .045" off the block to get the deck height where it belonged.Needless to say,the engine needed shorter pushrods and a distributor base shim. Also, .050" came off each side of the intake to make this whole thing work.

[Dwight Southerland]

An easy way to get in the ball park is to assemble the head, set it up so the combustion chamber surface is level (use a short carpenter's level and check it several planes), then fill the combusition chamber with the correct volume fluid (76 cc). Use a depth mike or a dial indicator on a bridge that is zeroed to the head surface and measure to the surface of the fluid. Do this on all the combustion chambers and figure an average. Subtract about .003" to account for the miniscus shape of the fluid in the chamber and have the machine shop cut that much. It will get you within .5 cc every time. Works on any head, not just a SBC.

[gmonde]

Originally Posted by Dwight Southerland

An easy way to get in the ball park is to assemble the head, set it up so the combustion chamber surface is level (use a short carpenter's level and check it several planes), then fill the combusition chamber with the correct volume fluid (76 cc). Use a depth mike or a dial indicator on a bridge that is zeroed to the head surface and measure to the surface of the fluid. Do this on all the combustion chambers and figure an average. Subtract about .003" to account for the miniscus shape of the fluid in the chamber and have the machine shop cut that much. It will get you within .5 cc every time. Works on any head, not just a SBC.

that is some great tech info learn something new every day gmonde

[Rich Biebel]

In the shop I worked at we had a factor written down for almost all common Chevy heads for milling. I milled and cc'ed every head you could think of for over 10 years. An old high compression head like a 461 was about .0065" per cc. A newer style open chamber head like a 441 was around .0058". Bigger chamber area/smaller factor.....smaller chamber area/bigger factor...

Those numbers are from memory......it's been many years since I did that work everyday....