I saw over on the .org site where Doug Dutra was telling someone that big block exhaust valves were a "better" choice for valves than 318 valves. He said the 1.81 or 1.74 exhaust as the intake and the 1.50 exhaust as the exhaust with some trimmed off. I'm still trying to figure out WHY he says that. They have .100" more stem length, which isn't needed. TO me the 318 valves are the better choices, since they are closer to being the correct percentage VS the bowls. The big block valves would make that percentage off balance, IMO. In any event, I am using the 318 valves.