While calculations show 500 CFM to be overkill on a 305 running at factory designed engine speeds, as with many things, calculations do not represent real world results. More than likely, the same engine with a 500 CFM carb will make more horsepower than the same engine with a 350 CFM carb, or the factory carb.
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Turbobill. I fully agree with you on that
Years ago I tested all 3 of these carbs on my 68 305E and the Holley 500 was still by far the top performer, it's all about the real world results