The 54-55 5913 head had a combustion chamber volumn of 86.3 or so cc. The 848 head is 79.1. The 848 head entered service in 56, along with the neoprene rear main seal. Tom Langdon and I were on the phone one day, has to be 20 years ago or better. He was still working at gm and he had access to the specifications and looked them up. He also gave me the specs for the two different 261 heads. I have measured a few heads and they all come up to about those numbers. Some a little more, but generally pretty close. So 8.0 for the 57 with the tighter combustion chamber is in the ball park. Where the extra 1/4 point came from 58 and up, I do not know.
Last edited by Dragsix; 07/05/2020 2:05 AM.
