[Chaplin]

MidOHasp-
You are correct in your thinking. 650 is not too small for a 350. I posted this in another thread, but here it is again.


A 350 with max rpm of 6500 and 100% volumetric efficiency (VE) (which you will not achieve with a naturally aspirated motor), you would need a carburetor that flowed 658.3 cfm.

How To Calculate CFM:
Engine size (CID) x maximum RPM / 3456 = CFM
CFM @ 100% volumetric efficiency

(Using this example: 350 CID x 6500 RPM = 2,275,000 / 3456 = 658.3)

Below is from Holley:
Most Street engines are capable of achieving only about 80% VE; a modified street engine with ported heads, headers, intake and carburetor can achieve about 85% VE; a fully modified race engine can achieve 95% or greater VE. The CFM number arrived at with this formula must be factored by this percentage.

Therefore, assuming you achieved the same VE as a fully modified race engine, (95% VE), the max CFM necessary would be about 625 (95% of 658). Therefore, a 650 should be fine for a 350. You certainly could use a 750, but you may suffer some loss of power and responsiveness on the bottom end because of decreased velocity of the air/fuel mixture.