Quote:

---

There is no "determined size".
The real question is "how much pressure differential do you want at WOT?"
Big carb = weak signal = difficult to tune, big power: 1" WOT vacuum.
Economy car = small carb = excellent response + good mileage: 3" WOT vacuum.
Very complex carbs such as Weber DCOE, Dell'Orto DHLA have good response and signal as low as .5".

Carb CFM is not a fixed number. A 750 only flows 750 is the engine demand produces the Holley test vacuum figure of 1.5 inches of mercury. If the engine produces more vacuum (2" etc.) carb flow increases, and vice versa.

Why does high WOT vacuum reduce power?
#1. pumping loss
#2. the VE is affected by the vacuum reading. No N/A engine has 0 vacuum, which means the maximum VE (absent wave/sonic tuning) is below 100%. Theoretical calculation is
((ATM - WOT loss) ÷ ATM)^.5

---