i know of guys running the 516 head with bigger exh valves way into the low 12's with just bowl cleanup, they flow enough for a good street strip type engine, i would put in the 1.74 exh valve on a 440, i run a 915 head in my 383 with the smaller 1.60 exh valve no biggie on a 383 but if it were a 440 i would want a 1.74 valve.