I agree with Diplomat360 as I mock-up assembled my big block without pistons and rods to check the radial clearance of the valves and cylinder walls. I got the BIG suprise when at maximum lift I saw how close the exhaust valve was to the cylinder wall. I should have done it earlier, before all the final machine work.The clearance did reduce as the lift increased. I ended up with .030" radial clearance at max lift.No room for a bigger valve there. This dimension doesn't even take into account for any growth or deflexion due to heat or RPM. I really got lucky here. Engine is iron big block, 4.350", .690"lift solid roller w/Victor Max Wedge heads. More lift or smaller bore and there would be trouble.The point of the least clearance was in top ring territory, so no wall reliefs there. I'm sure that there is some valve shrouding effect here. The intake valve had, visually more radial clearance.I used a round wire gauge to accurately check the clearance. ( Miked a paper clip!) Bill