Ok, so because of the delay in opening the outer carbs as well as the jetting on those outer carbs that is how they can run 960cfm on a smaller cubic inch engine?
By using three 2 bbl carbs that open at different times and are jetted differently, the total airflow and A/F ratio is optimized so that it is never oversized at low rpm and never flow restricted at high rpm.
It would be like if you could use your 600 cfm 4 bbl at low rpm and then switch to a 750 cfm at high rpm.