4 Barrel on a stock slant

The problem is the cfm the formula gives which are pretty close to what the engine actually uses but a carbs cfm is a rating doesn't actually correspond to the formula numbers. Just like head cfm it's a different rating also.

Take a built 700 hp block that needs a 1000 cfm carb but instead you bolt on a 500 cfm 2bbl (which would even be rated less if rated like a 4 bbl) but that engine will still pull close to 1000 cfms through that 2 bbl but obviously cause of restrictiveness will make less power and use a little less cfms.

Why not just measure it, like I said earlier run a vacuum gauge on the engine do a full throttle run and see what vacuum the engine is pulling if 3 and under a carb switch is unlikely gonna help much.