The Stovebolt Site Forums The Shop Area Engine Shop dual carb 261 setup

All,
Have been trying to find setups for dual carbin a 261 with limited luck. Was wondering what would run on this motor?
My brain 261 setup -
1952 3100 seris pickup
Standard 4spd floor shift
1955 261
1958 848 head - polished ports and unleaded valve guides?
mild cam - 210 degree duration at 0.050 lift
Dual Fenton Exhaust
Dual tattersfield w/ 574S carter W-1?


Thoughts are welcome, including other peoples setups....
Thanks in advance .....

I have tried:

Dual original one-barrel Rochesters - too much flow (a little rough) at low RPMs but good response at high RPMs.

Dual progressive two-barrel Carter-Webers - no enough flow at high RPMs

SWEET has a nice set-up - I think he has dual carter one-barrel carbs (from 216s?)

I now have (two weeks of use) a single two-barrel Holley AA-1 carburetor that was used on GMC 270/302. It has variable jets. It has good top-end power and smooth low-end idle/response.

Now granted, there is romance in multiple carbs, but a good streetable set up would be a plain ol' single four barrel set up. IF you could find an intake. But inlines are an easy animal to feed. A homemade intake, one out of tubing aint too hard to do. I had a buddy back in high school days that butchered a stock 235 intake and made the heat riser "box" into a four bbl intake with just a flange plate and no step down adapters. He sucessfully used a WCFB Carter off of a '56 Chevy. It ran nice on his 243ish size (235 bored .060") engine. No doubt one of those would go well on a 261, as you would have smaller primaries than any of the dual single bbls have giving you better drivability. The WCFB Carters have a weighted air valve on the back barrels so when you floor it, the back two bbls dont come in until the airflow is enough to swing this valve open. They worked great on 265 V8s and carbs dont know whats under 'em, so a 261 is well in the ballpark. Some factory 265s even had two WCFBs-again "no hill for a stepper"(261). Being able to just bolt on the proper intake would be a definite plus. Your lower pickup gearing would hide any small stumbles during off idle transistions. my thoughts.

Thanks guys for the feed back. I'm hopping to keep the tattersfield, it looks way to neat to sell off...I have never seen a four barrel on a I6, never knew that was an option......

Now, I dont see it mentioned around here too much, but everyone seems to think two stock carbs is a bit much. Lets explore what the conservative old Chevrolet factory boys did on the Corvette automatics. Those 'Vettes ran THREE Sidedraft Carters on their 235s with only PowerGlides and 3.55 gears(sayin' that higher numerical gears make it easier to tolerate overcarburation). I've had that set up on a 261 with happiness, and driven an old '54 stock 'Vette and found it pretty peppy for an old PowerGlide car (almost lay rubber taking off). Those set-ups are now rivalling gold in pricing these days. Now, I bet they might not have been the same size per carb as a sock model B Rochester, but there were a line of them three deep. Those Carter YHs were very primitive and had no vacuum actuated power stage-just linkage that yanked the metering rods into their power stages per throttle position only and all three acted simultaneously (not staged). Go to the Inliners site and check out the technical tips department and look for tips on living with multiple Model B Rochesters-its good reading.

It was probably over on the Inliners I was reading, but isn't one concern with 4B on inlines, equal distribution to each intake port and pooling when WOT at load... or something like that?
Anyway edski's right... they have the dope over there.

Are people around here concerned about multiple carbs being too many carburetors ("a bit much") or the total CFM of multiple carburetors being "a bit much"? My post above reflects my belief that too little or too much CFMs affected the performance of the various carburetors I have used with 26!s.

A post on the H.A.M.B suggests that the 235 Corvette Carter YH side-draft carburetors were each rated at about 130 CFM (a lower single-carb CFM compared to a high-pressure 235's single barrel Rochester). The Corvette's three YHs should then result in about 390 CFM, which is just a little higher than what Clifford's calculated for my 261 (over-bored 060", with dual headers).

One potential advantage of the multiple carburetors is a more even distribution of fuel to all 6 cylinders.

After successfully running different dual carburetor set-ups on a 261 (bored to around 270), I planned to try single carburetor set-ups (all rated for 400 CFM or less): Holley AA-1, Rochester 2GC, Zenith used on a GMC 270/302.

The Holley AA-1 (two-barrel with variable jets) seems to be working nicely, so the good results from simpler plumbing will suit my needs/interests for a while.

The corvette set-up on my .060 over 261 was just ducky year 'round (though Texas dont have too many challanging winter days) it did its job on my daily driver. My particular setup was of course, second hand and had the choke linkage sawn off its rear carb as is typical when used on non-corvette vehicles (firewall rib interference issues on a lot of '49/'54 cars). But as run with only two choke equipped carb start up was as normal as with the stock Model "B". What ever CFM rating at whatever mercury pressure, the number of carbs and and their total cfm rating was right on for an approx 270 motor on the street. They really had a neat "roar" when opened up-sounded alot like a split manifold exhaust only thru the carbs. An approx 400cfm four bbl carb would be good as you would be running off the front bbls (sort of half the size)continueously and only bringing in the rest of the gang upon demand.
A question- what are "variable jets" you dont mean the idle mixture screws do you?

Strictly in the realm of idle speculation:

Carter did NOT publish a CFM rating on the 2066s type YH carburetor(s) used on the 6 cylinder Corvette. Chevrolet was happy with them, and it wasn't anyone's else's business

However, the main venturi was 1 5/16 inches.

In Doug Roe's book, a monojet with 1 5/16 inch venturi is listed as 210 CFM.

1 5/16 translates to about 33.3 mm. Zenith shows a size 3 carburetor with 31 mm venturi as flowing 210 CFM, and a size 4 carburetor with a 34 mm venturi as flowing 220 CFM.

All of the above would be at 3 inches of Hg. Converting to the 1 1/2 inch Hg (4 barrel scale):

210/1.414 = 148 CFM
220/1.414 - 156 CFM

CFM in a multiple carburetor setup is not "additive"; you have to throw in the IFF (a.k.a. International Fudge Factor ;)) which varies for different manifold designs.

As stated above, idle speculation.

As to the 4-barrel, I put 400,000 miles on a different make (rhymes with Cord) 300 CID 6 using an Offenhauser intake and 400 CFM Carter AFB (number 9400s). The engine exhibited good drivability, and the fuel economy normally associated with Carters.

Jon.

I should have called them adjustable main jets (allowing variable settings)? I think they are like these adjustable main jets.

Thanks for the info so far everyone.....side bar, OJ is about to put a pair of old Zenith 1937s to get me by on my 235 until I can get my 261 put in.....

I just set up a dual 1bbl TBI injection set up for a guy with a 57 chevy.
It's getting installed as we speak so then I can get the final tuning done on it.

Let me know if you can't see the pics by clicking on them.

Electronic distr conversion for timing control.

http://www.binderplanet.com/photopost/watermark.php?file=18049

http://www.binderplanet.com/photopost/watermark.php?file=18051

Throttle bodies and adapters.

http://www.binderplanet.com/photopost/watermark.php?file=18053


http://www.binderplanet.com/photopost/watermark.php?file=18054

That TBI should work great! I replaced my points and coil with plantronix. They seem to work ok but, have not noticed any difference. Minus cleaning and adjusting the points :-)....

My 52 is about to get a tattersfield and zenith carb install....

http://i1069.photobucket.com/albums/u462/52Stove/IMG_0381_zps4e0e5cc2.jpg

A set of air cleaners

http://i1069.photobucket.com/albums/u462/52Stove/IMG_0392_zps76164e95.jpg

A set of Zeniths

http://i1069.photobucket.com/albums/u462/52Stove/IMG_0540_zps11c80afa.jpg