You are just flowing the bare airflow past the throttle blades. You can make up any numbers you want if you do not flow liquid thru circuits that have liquid/air flow thru them in normal operation. Carbs are wet flow tested if the testing is done properly.Ĭhanging the flow test pressure from 20.4 inches of water to 28 inches of water was a marketing gimmick by Barry Grant to sell his carbs at a inflated airflow rating to get more sales vs the Holley carb, Carter Carbs, and Rochester Carbs competition. If you do not know how to test the carburetors properly then you should not be working on carburetors or testing them on dry flow benches. This is why a Holley 2-Barrel carb rated at 500 cfm air flow will flow a lower air flow number at 20.4 inches of water test pressure/1.5 inches of mercury, and obviously a third WRONG flow number at 28 inches of water test pressure like some cylinder heads are tested at. If you have a Superflow flow bench that cannot generate 40.8 inches of test pressure across the flow passages of the 2-barrel carb (with liquid in the fuel bowls) you are testing the carb improperly to get an accurate flow number. 1) 4-Barrel Carbs have been (before World War II) tested at 20.4 Inches of Water Test Pressure which is 1.5 inches of Mercury Test Pressure.Ģ) 2-Barrel Carbs have been (before World War II) tested at 40.8 Inches of Water Test Pressure which is 3.0 inches of Mercury Test Pressure.
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