Ran a set of 325cc 440-1 heads cnc'd for an entire season.. Car ran average of 4.72..Took the heads off last winter and did some hand porting and a little reshaping of the bends and combustion chamber and as of right now the average ET is 4.67..And that was me doing it by myself without a bunch of fancy equipment..Just a die grinder and sandpaper..So i'm sure a shop with a more knowledge can make a cnc'd set much better by hand. Just saves alot of time not starting from scratch.