The 848 head was introduced for the 1956 pass cars. I have one that was cast late 55 so for the 56 production. I am not sure if they were ever installed on a truck motor, although they were installed on the Canadian Pontiac 261 pass car motors. A lot of years ago now, I was on the phone with Tom Langdon while he was still at GM and he looked up some head casting numbers for the chamber cc. The 848 head was theoretically 79.1 cc. The compression ratio for the 56-57 passenger cars was 8.0 to 1. That ratio was upped a little, 58 I think, but 59 for certain, to 8.5 to 1. I have never cc’d a 56-57 head and a 58 and 59 head to see if there is a difference in the combustion chamber volumn, or the piston to deck height of the various year motors to see if there was a difference. So I don’t know why the difference in compression ratio. At any rate, every one wants an 848 head to get that supposed .5 compression increase.
