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Valves have to be steel with a standard 0.34375-inch diameter stem. The maximum valve size is normally Chevy standard 2.020 inches for the intake and 1.625 for the exhausts. One trick you can do, however, is used undercut valves. It’s hard to see here, but the darker portion of these Ferrea valves is actually 0.3125-inch. This is the portion of the valve stem that stays below the valve guide. The smaller diameter not only reduces the valve’s weight but also creates room in the lower portion of the port to allow for more air and fuel to enter the combustion chamber.