Hey Folks:

I am considering building a dual inlet carb plenum, due to height restrictions with engine cover. That said, I plan to use two 3" inlets. But I am not sure if the CFM that can be drawn through that diameter pipe (x2) is enough for my Holley 750 DP. Anyone know how to calculate CFM for a 3" pipe?

Cheers JC71

well measure the diameter os each barrell, will be something like 1 3/4 inches.
1.75 inch has an area of 2.4 sq inch. you have 4 of these. so you need a total of 9.6 sq inch minimun.
a 3 inch pipe has 7.06 sq inch, so 2 of them will have over 14 sq inch, basically 50% bigger, less bends and so on, tells you it will be fine.
Also i think your throttle bores will be LESS than 1.75 inch each.
hope that helps
Paul