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Flow bench testing is an easy way to discover how bore size affects airflow and performance. If you want to increase the airflow of even a simple small-block Chevy cylinder head, just change the test bore size adapter from the 305's 3.735-inch diameter to something like the 400's stock 4.125-inch bore. This could be worth 10 cfm at max flow. If you watch closely when cylinder head companies state their flow numbers, the smart ones will use a larger bore to improve the flow numbers.