Daniel.  This answers your question that was under the heading “YBM alum head photo’s”.   It’s a new topic so I’ve taken the liberty in starting a new thread with it.

A 3cc variation is still normal even in the newer oem castings.  Combustion chamber size control or variation by the oem’s hasn’t changed much in the last fifty years.  A case in point is the combustion chamber volumes varied so much on the FE’s when they were first introduced in 1957 that it forced all FE heads for the first half year of 1958 car production to have the combustion chambers machined until the casting techniques became stable enough to permit the combustion chambers to be used as cast.  I just recently did a set of new 502 BBC (scrub) aluminum heads and there was a 3½ cc variation from end to end on one of the heads and a significant difference from head to head.  Needless the say, the customer was not happy but the heads were easily fixed with a little time and perserverence.  Some (not all) of the aftermarket heads are surprisingly close so the control is there if need be but many of the oem heads still exhibit a combustion chamber cc variability that would appear to be excessive.

In summary, the same core shifting that occurs with the cylinder walls of a block is also present when casting cylinder heads.  Where this core shift is in regards to the reference points in starting the machine work on blank head castings ultimately plays a large part in what the final combustion chamber cc’s are going to be.  On a performance build, I will cc each chamber of both heads being used and then correct as deemed necessary so all chambers are sized the same.  More often than not, the combustion chambers will be progressively larger in cc’s from one end towards the other.  In these cases the calculations are performed so that the heads are angle milled end to end so that one end is milled heavier than the other which in turn allows the combustion chamber cc’s to be more equalized over the length of the head.

Lorena, Texas (South of Waco)