The polysphere motor predated the big block Chevy by several years (1956 277-1963 G.M. "Mystery Motor") and utilized canted valves set at different angles, a first for OHV V8's. It could be said that that first Mopar "A" engine was a "prototype" for the later Big Block Chevy. That A engine was an outgrowth of the previous Hemi motor; an attempt to retain some of the advantages of the Hemi combustion chamber, without the expense of two rocker shafts and such a really wide cylinder head. It was the first "semi-hemi."
