Inliners International Forums General Discussion Engines Rochester "B" Carb sizes and cfm's

With a couple recent posts referencing this I will list what I *think* I know about the "B" carbs though I am still learning.
I have written an approximate CFM estimator so I have guessed the CFM's at 1.5" Hg (the 4v standard). Comments, corrections, additions more than welcome I am trying to slowly get the history right.

*Guessed CFM at 1.5" Hg
*Guessed CFM at 3.0" Hg
*Venturi
*Throttle
*Jetting

Smallest - application is "optional" 235 truck and 230 car, I am guessing either economy special or taxi?
113cfm at 1.5"
158cfm at 3"
1-1/16 vent
1-1/2 throt
Jet #42 to #44

Next - listed as the "216" carb in recent post
137cfm
191cfm
1-7/32 vent
1-1/2 throt
Jet #51 to #52

Next - carb on most of my 194, 230, 250 Chevy II's, same size used on the 235 per panic below and also per tocmp 32-62chevy
153cfm at 1.5"
214cfm at 3"
1-11/32 vent
1-9/16 throt
Jet #57 to #58

Next - I thought there was a 1-13/32 venturi in the May 55 Hot Rod article but actually I think it is the one cited below at 1-15/32:

Next - cited on this forum as the 54-63 261 carb, also I think this is the one in the May 55 Hot Rod buildup
182cfm
254cfm
1-15/32 vent
1-11/16 throt
Jet #64 to #65

Next - the carb I find on early 292's, I think it was also used on the "HiPerf" 230/155hp in 64.
196cfm
273cfm
1-9/16 vent
1-3/4 throt
Jet #70 to #72

Some of the jetting info came from:
http://www.newagemetal.com/pages/Chevrolet/32-62Chevy.pdf
It is consistent with the jets I've found in the B, BC, BV carbs.

As I said all the cfm's are my guesses/calculations, the calculator thing is typically accurate within 6% on carbs from the Rochester "B" to the Holley Dominator. Best I can do, if anyone has some cited CFM's for these or knows more about the applications that would be welcome too.

Thanks.
I concur on the 216 & 261 sizes, don't know of use for the smallest one.
AFAIK the 235 is also 1-9/16" × 1-11/32" (this is the one McGurk says is too big for dual use on a 235).
I found a 1-3/4" × 1-5/8" also.

Can you give us any details on how this was calculated?
Do you allow for the booster?
Throttle shaft diameter?

Calculation is pretty empirical based on venturi, throttle, booster od and id, and a factor for the choke plate. There is also a factor for the "smoothness" of the entry, for example some of the modified Holley's with no air horns and everything super smooth. These last two "factors" are empirical and just set by looking at the shape, and then they are related to the other sizes (venturi and throttle). After tuning this little program on everything from the Stromberg 97 to the Holley Dominator, it is pretty good if I have a picture of the carb and the venturi, throttle, and booster measurements.

I think I've found an anomaly.
The usual rule is that the SAE flange size covers a specific range of throttle disc diameters with no overlap (the same throttle disc won't be available in 2 different flange bolt patterns).
Except: the 1951-52 Pontiac Model B is 1-1/4" SAE flange (2-11/16" like the 216), but 1-9/16" throttle disc (like the 1-1/2" SAE 235 & 261 but with 2-15/16" flange) and 1-5/16" venturi - a size not offered in that bolt pattern.
Looks like Pontiac has a space problem, or a lot of manifolds already made with SAE 1-1/4"? Misprint in the official Delco sheet?

In the for what its worth category, CFM ratings were published for some of the Monojets:

1 7/16 throttle 1 7/32 venturi - 160 CFM (113)
1 11/16 throttle 1 5/16 venturi - 210 CFM (148)
1 11/16 throttle 1 1/2 venturi - 250 CFM (177)

All ratings at 3.0 inches Hg. I calculated a factored 1.5 rating which is listed in ().

Jon.

Does anyone have a source of jets for a Rochester BV? Once I start racing my Chevelle I plan on trying different jetting. I'd rather buy if I can rather than make them.

The Rochester 2GC 2bbl uses the same jets as the B 1 bbl

http://www.carburetion.com/r2.htm

http://www.carbsonly.com/

I didn't know the 2gc was the same, nice tip!

I've tried filing down the front face of a Holley 4150 jet so it clears the bottom of the "B" bowl, and that worked well - it wanted about 3-4 numbers bigger than a comparable "B" jet but ran good. That way you could get any size Holley jet you want. Problem is, see sizes above, most of the "B" carbs used jets of #58 or thereabouts which would mean about a Holley #62, smaller than the ones in the bulk jet assortment. But for the larger "B" carbs using a Holley jet might work if you do a lot of tuning.

I run Rochester 2GC carbs on my HAMB dragster and I bought a 1/4 X 32 tap and tapped out the Rochesters and use Holley jets now.

Ron