valve guide specs

worth noting is that all modern engines have valve seals on int and exh valves.

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Overhead cams, high flow lowish pressure oil perhaps.
Cash

Wonder if the exhaust seals work opposite of the intake seals and prevent case pressurization from blow-by rather than oil control? Seems like pressure in the exhaust port would be all positive.

A main reason for exhaust valve seals is due to the venturi effect of the gasses rushing from the cylinder out the exhaust and sucking oil past the valve into the exhaust stream. It can end up putting substantial deposits on the valve stem, disrupting air flow in addition to "burning oil." Of course, the engine is not burning it in the combustion chamber but it is "using" oil and will smoke pretty much like an engine that is burning it in the combustion chamber.