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Sometimes in the pursuit of airflow, greed can get the best of any porter, and the tendency is to go too big in some places. Nowhere is the price to pay higher than going too big in the port throat, the point of constriction just below the valve seat. Make the throat too big, and the venturi effect is ruined, and usually the flow will be too. Keep the intake port throat no larger than 90percent of the valve diameter, and the exhaust throat down around 85percent.