the 6pak/6bbl needs to be thought of as a vacuum secondary 4bbl with 2bbls added. those carbs should never be thought of as three independent carbs; which is the way holley currently rates the air flow. 1350cfm is a bogus marketing ploy. if i remember correctly the original flow rating was 1030cfm. cfm ratings have become a manipulated marketing ploy. i don't know why people take them seriously.