Rochester 2GC CFM?

Anyone know what CFM ratings are on these, I think the small base is 1-3/32 bore, the large is 1-3/8. I'm thinking about doing a 3X2 for my 472 Caddy and I'm wondering if I need large or small base?

 

As I understand it they are 280 CFM.

 

I don't know about the sizes you mention, but in oval Street Stock racing everyone wants the 1-11/16" throttle bore versions. They had 1-1/4" and 1-3/8" venturi bores.

If the track allows it, the 1-3/8" venturi version is supposed to flow about 500 cfm (about equal to the Holley 4412 two barrel which is also common for oval cl***es). Many tracks with limited rules don't allow Rochesters with venturis bigger than 1-1/4" which would flow slightly less, probably between 425 and 450 cfm.

Keep in mind that 2 barrel carburetors are rated at a different vacuum than 4 barrels, so a 500 cfm rated 4 barrel actually outflows a 500 cfm rated 2 barrel. The 2 barrel would actually flow about 390 cfm when the difference in vacuum at flow testing is factored in.

 

Most of my experience has been with Pontiacs and SBC's.
A "normal" setup for a 3X2 would be a small bore for the center and large bores on the ends and a progressive linkage.
With a big airpump like the 472 I would think you would want a big bore in the center too. Of course, it all depends on what manifolds are available. I dont know CFM rating but I suspect you might only have about 600 + max with all carbs wide open, if that.
It's the old question do you want to look cool or make big power? The two don't always seem to go hand in hand. (blowers excluded)
Of course you could go really nuts and fab up a dual log or single plenum manifold and put 4 or 6 or 8 of those bad boys on there. (good luck tuning it)

 

I don't think any manifolds are available, but I do have a cast iron single plenum intake from a 425 that I am thinking about cutting the top off and weld on a new mounting base for the 3X2, I am doing this mainly for "the look" but it does have to be functional.

 

i have 2 rochester 2g's on my 287" pontiac...running straight linkage.
these are small base 2g's, and my motor is bone stock. it runs great, idles great and pulls pretty good for what it is. of corse, i'm only running 2 of these (no idea what size the throttle bores are). if you run progessive linkage (at least this is what i was told) the secondary carbs, have to have the idle circuits blocked off, and they need different throttle ****erflies (so they close 100% and don't let any air in when they are closed). so, the secondaries are dead until the throttle is openend all the way. they are considered 'dumper" carbs, because they do not contribute to the engine idle...it idles off the center carb only. this is what i was told, don't know how true it is, i've never built a 3x2 set up. my 2x2 set up idles off of both carbs, and they work together as one...it works great in my opinion. it doesn't run or idle too rich. the carbs i used are 1955 rochester 2 gs, and they are pretty small in physical size as compaired to 70's rochester 2g's.