Ron, I am using the as supplied 2.20" int. & 1.81"exh. valves that came with the Edelbrock Victor heads w/ an extra half thou. guide clearance added per recommendation by Kris at Nelson Competition.Most race time will be during the the hot climate in Florida.My thoughts are that radial cyl. wall/exhaust valve clearance can be tighter than piston to valve radial clearance due to the fact that piston and aluminum rod growth don't enter the equation. I am "all good" with piston to valve clearance.Has anyone else used Edelbrock Victor heads on a big block with a 4.350 bore and .690" lift cam? Thanks, Bill