you can approximate the two cfm ratings (and be good 'nuff for gov'mt work) by taking the two bbl rating (taken at 3" hg. pressure) and multiply it by 0.7 to get what it would be by the four bbl standards (taken at 1.5" hg pressure). Or take a four bbl rating and multiply it by 1.4 to get the equivilant two bbl rating--thus the highly glorified holly 500 cfm two bbl carb becomes a 350 cfm carb in four bbl talk, much like some large base Rochester GCs. this information can be found in the Rochester carb book written by Doug Roe a Rochester engineer-can still be bought at Amazon--for older rochester information try to buy one of the older printings 'cause the latest printing (has a an electronic q-jet picture on the cover) starts favoring the later carb stuff. earlier printings have good Model "B" stuff.
As for sizing, the old Corvettes had THREE one bbls (non-progressively arranged) and used only automatic transmissions(where no favoring could be had by slipping a clutch) and worked beautifully--I've driven an old 'vette, and had the set up on a stick shift 261 also-they did a good job in both situations with stock jets.
Last edited by edski; 09/23/2013 10:47 AM. Reason: vette stuff
