carb cfm ratings

It seems I might be losing it
Does anyone know how carbs are cfm rated and how 2 bbls are rated differently than 4 bbls and what the conversion factor might be.
I am specifically interested in converting a 230 cfm 2bbl to 4 bbl equivalency and specifically interested in re-rating a 650cfm 4 bbl to a 2bbl equivalency.
My brain has temporarily misplaced this information.
Many thanks to any helps