First of all ,2 and 4 bbls are cfm rated using different test procedures.To compare the two,divide the 2 bbl cfm rating by 1.4, so the 500 cfm 2 bbl is really equal to a 360 cfm 4 bbl. The old Carter 4 bbl used on 283 Power Pak engines was rated around 400 cfm so...Q-Jets flowed around 650 to 800 cfm depending on application. In theory ,the Q-Jets air flap on the large secondaries will only flow as much air as the engine needs. In reality,the small primaries have you constantly opening the secondaries to get any power.
Some will say the large throttles of the Holley 500 2 bbl have poor throttle response compared to a 4 bbl with small primaries, but it ain't necessarily so if you do side by side comparison tests.
