Better head
"Later, a five-pointed star was used to denote the special head for use with the aluminum block, which had slightly smaller combustion chambers and tighter control of combustion
chamber placement to assure proper head gasket sealing. This was necessary due to the relatively narrow area available at the top of each cylinder liner for gasket sealing. For the 1963 model year, the tighter placement control and smaller chamber diameter were communized on all Slant-6 heads; any '63 or later cylinder head can be used on an aluminum 225.."
Hard to believe a head combustion chamber could be 'moved' in an existing casting but it sounded like it was a new casting altogether with a smaller CC area to completely cover the cylinder edge, not an old casting with a potentially larger CC footprint. Interesting...kinda sounded like a sketchy design from the start with that small of a fire ring area.
Money shot:
"Later, a five-pointed star was used to denote the special head for use with the aluminum block, which had slightly smaller combustion chambers and tighter control of combustion
Hard to believe a head combustion chamber could be 'moved' in an existing casting but it sounded like it was a new casting altogether with a smaller CC area to completely cover the cylinder edge, not an old casting with a potentially larger CC footprint. Interesting...kinda sounded like a sketchy design from the start with that small of a fire ring area.
