Rochester 2bbl large base vs small base dims ??

Hi,
anyone have info on the size of the bases for both small and large base Rochesters ? I'm discussing somer with a guy at the moment but with out seeing and measureing myself I'm not too sure which he has, anyone got some dimensions or info ?

thx.

 

The small ones have 1 7/16" throttle blades.
The flange bolts are centered on a 3 1/4" X 2 7/8" rectangle. I don't know about the bigger ones sizes. Smokey

 

Anyone ? someone must have a pic or diagram of bth or at least measurements ??

 

back tothe top someone must have some good info on these things....

 

I measured a big base as 3.67" X 2.00" measured from the center of the holes.

 

cool thanks for tat will check against what I have.

 

The small base come with a side inlet or front inlet,they flow 280 CFM. All side inlets were small base no side inlets were made in large base.These are the ones usually uses on tri-power setups. They came on among others 64-70? chev and other GM.

 

I think the small base ones were used in various forms throughout the whole production run and the only one you probably couldn't use in a "normal application" would be the one for the Vega (remember those?) because of the reverse power valve.
I first remember seeing the large base one used on a 57 Pontiac I had. The largest venturi models could be found in Pontiac and Buick models sporting very large displacement single two barrel V8s in the late 60s and early 70s.
The first GM four barrel was the Rochester 4 jet and was basically 2 of the small base 2Gs in a common housing.
As for TriPower (a Pontiac term), Pontiac and Olds used 3 of the small base carburetors in 1957-58, Chevrolet used 3 small base ones on the 348s around 1958-1960, maybe 1961. Pontiac used a small base carburetor in the center and the large base carburetors at the end positions from 1959 to 1965 as did Cad around 59-61. In 1966 Pontiac and Oldsmobile used large base carburetors at all three positions. Remember, if you're after real TriPower carbs there's more to the end carbs than just base size (bases, throttle blades, specific throttle arms, etc.). Much written here previously, especially on the TriPowers, just search the archives. Tons of info out there on the web too, whole sites devoted to just these setups.

 

good info

 

Although this post is old....I found this today & thought I'd post it:

From a company called L.L. FULTON Inc.- Great Falls, Montana
(I think they specialize in Rochesters)

FAQ Section --> "What Size carbs do you use?

We use the Small Base Rochester 2GC Carbs in ALL but a few of our applications.
- The Small Base Carb is ID’d by the air cleaner flange diameter of 2 5/8”.
- The Large Base Carb is ID’d by the air cleaner flange diameter of 3” or 3 1/16”.

http://www.hotrodcarbs.com/faq.php#sizecarb


Thought it may help somebody else.

 

If you don't have a tape with you, look at the oddly shaped exhaust gas passage that runs along the top of the base from one side to the other with the mounting bolt holes going through it. A large base Rochester does not have this passage. Very easy to identify if you know what to look for.

 

go to the parts store and get a couple carb base gaskets, one for a 70' chevelle with 307 2v and one for a 75' chevy pickup with a 350 2v. chevelle will be small and pickup large.