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The bore is 4.365 (.040 over on a 440). And yes, the bore is bigger than the chamber in the head. The 0.075-inch measurement is from the head gasket surface to the quench pad portion of the combustion chamber in the cylinder head. That is measured by putting a straightedge over the gasket surface of the head and sliding feeler gauges underneath.

I figure I can squeeze a little more compression out of this motor, since I'll be running a fairly big cam with a late intake valve closing event. I don't have that spec in front of me right now, but I've run 10:1 on an engine with a cam that had an earlier intake closing and had no detonation problems.



You need to round that edge over or you have the potential for a hot spot that will cause preignition. General rule of thumb is .005 for evry 1cc on a 906 so you need .0025 off to get your half point compression.