I cant remembered the conversion formula but a 500 2bbl is equal to a 390 4bbl.
A 390 2bbl is just front half of a 650 4bbl and 500 2bbl is just front half of a 750 4bbl.
If that helps.
So, if that is true,
and the 500s are rated as 2bbls, then One would expect half a 750 to flow 375 when rated as 4 bbl. Since it is rated at 500,this is 500/375=1.33 times as much. That would lead me to believe that a 230 would also flow 1.33 times as much, becoming a 307cfm.
But in regards to the 390/650 it muddies things up even more. Half of 650 is 325. But 390/325= 1.2, and now my 230 is just 230 x 1.2=276cfm
You see what my dilemma is?
So my guess would be the 230 2bbl would be 180 4bbl and a 650 4bbl would be about 800 cfm 2bbl.
But really what cfm your engine uses is what cfm your carb will be no matter what you run. like that 230 2bbl will pull a 1000 cfms if you make to but will eat a lot of hp and might not function to well.
