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Message: <blockquote data-quote="shiroitenshi" data-source="post: 1337908" data-attributes="member: 27518">You're quite right on that point, but the reason is that if we're running oversized valve sizes, there might not be enough clearance in between when both valves are at their max lift. which is why most manufacturer of cam specifically states that oversized valves should not be used with their high lift cams. I think only those specially manufactured heads have deeper valve seats to prevent this problem, though I'm not sure how much lift it allows, as I've never seen a dart-racing CNC'ed head with recessed valve seats in real life before. I think both crower and toda have this same disclaimer in their manual/catalogue. And I wouldn't say so about the valve will never hit high comp piston. At high revs, the rod actually stretches a bit and with a high lift cam, ker-thunk! Bye bye head.. (hence the required minimal clearance) It happened to one of the civic enthusiasts group I'm in (not an official group, just like minded people) when he bounced on a bump, misshifted, and the rev meter went well past the meter marks , over 10K i think, and thonk! 4 cylinder engine became 3, and somehow the engine died immediately. No broken rods, but damaged a B18C piston, broken valves, damaged head, B16B cam lobes got a piece chipped off (bye2 cam). Luckily he opted to tow the car immediately after that, or there would have been more damage as bits of vavles started traveling into the manifold and into the other combustion chambers. Seems like (in my opinion, that is) we should have a safe zone clearance value depending on rod material, (and those aftermarket ones usually tend to be a lot more resistant to stretching,  Thanks for the claying info... sure is a creative way to test clearances.. Too bad it requires disassembling the head though. No biggie though. Thanks for the head's up.I'll give it a shot. Thanks again.</blockquote>