As for the carb, the air flow required by any piston engine is related to the amount of air the the engine requires, i.e., internal cumbustion engines are air pumps. The air requirement is calculated as follows:
((CID x rpm/2) / 1728) x VE
In the case of our 200ci I6's, the factory NET HP rating is 91 @ 4000rpm. So, if the engine were 100% efficient (a VE of 100% - not a chance) the cfm requirement would be 231. While I don't mean to offend you (I have one also), the stock log head is very inefficient. My analysis says 75% is the correct number. So, 231 x 75% = 174cfm. Bottom line, you need a carb with a minimun flow of 174cfm on your car. The stock 1940 flows approx. 180cfm. Marginal at best. Since you have a header and upgraded ignition you have probably improved the efficiency of you pump enough to be too much for the 1940. Having said that, do not rush to the bigger is better side (the dark side in my opinion). Both carb volume and velocity need be considered.
Simply stated, HP requires intake volume (high rpm, big flow, - head and cam to match). Torque rsponds better to intake velocity. As produced, our cars are built for low end torque. Why? As an old saying goes ...you race HP, but you drive torque... So, when you are ready for your carb upgrade I think it hard to beat a progressive 2V like the Holley 5200 or the Weber 32/36 on a street car. The progressive design helps to keep velocity up as it runs on one venturi until the rpms come up enough to handle the extra volume. The 5200 flows 270 cfm (will support 5000 rpm @ 90% VE - probably never see 90%) and has a total venturi volume of 1.77" vs. the carb bore volume of 1.77 for the stock 1.5" head (through 1969),and 2.40 for the stock 1.75" head (1969 "M" and up). The 32/36 Weber flows 320 cfm and has total venturi volume of 2.9 sq. in. So, I wouldn't use this one on the early head. Actually, I have a hard time justifying the 320 cfm on a car that is used on the street. On the other hand, if you are building a car that is going to be expected to come out of the hole at 3000 rpm and shift at 6000, volmue will be king. A 500cfm Holley 2300 would probably work well on such a car, but only if prepared like Mustang Gezeers.
