It's just one of those rule of thumb like 2 hp per head cfm,
So take that 616 hp the other formula came out with and times it by 1.4 cfm
1.4 cfm x 616 hp = 862 cfm
use the formula peeps uses for carb selection but shouldn't cid x rpm / 3456 = cfm
So 862 cfm x 3456 / 589 cid = 5057 rpm
Gives the same basic answer at least on this one, formula is probably based on the 1.4 cfm per hp, quicker to use 1.4 rule of thumb especially if you good a guesstimating peak hp rpm. No formula is gonna be accurate a high percentage of the time ballpark is best we got.
