what to do with my 273

the 273 head is the one to use. it will flow about 158 to 160 CFM @25 " test.
the 302 flows less in the curve vs the 273 head. at .500 302 is little better.
the area from .050 to .400 is where the valve spends most of it's time. this is when the motor needs all the flow it can get. this is on a 920 casting head. the 360 valves are shrouded by the bores, causes flow loss.