I was fortunate enough to come across a 60's era Say-why-and 2x4 set up. It has two cater AFB's . One is a 3721SB H5 and the other is a 3721SB C5. I have read they were for a 300 hp,327. This makes sense, because of the owners car it came off of. The question I have is what would roughly be the Cfm rating of these carbs? I have measured the venturi, and they are 1 1/8 in diameter. I've read on this site that 575 is a possibility. But on another, I googled, they said a 1 1/8 would be a 400 cfm. Will I need to run two separate fuel lines to each carb, or can I do a fuel rail style line? Lastly, is this too much carb(s) for a 290hp 350 Chevy? Thanks for any Info!
id say they are 425 or so cfm id run two lines and i think it maybe too much for your engine if you run em remember afb's dont like alot of fuel pressure
Thanks for the reply.I plan on running a regulator, just want to know if I need to get one for each line or would one work to do both. I'm not going to be doing any serious racing with it just some occasional stop light fun. Came up with another question, anyone recommend a good cam for said intake set up?
Those carbs work great in a 2x4 application. I ran 2 3720 Carter AFB's on a 327, they worked great. A rail style line will work fine, sounds like a mild engine so there is really no need for two lines. You may have to go a step larger on the primary jets, stock rods work fine. If I remember correctly I ran .095 jets in the primarys. Good luck.
i guess its a personnel opinion thing but id run the two lines with a seperate regulator for each carb just to make sure they are "even"
Thanks guys! I'm open to all info. Like my name says jack of all trades, master of none. I'm learning as I go with the engine side of things. Paint, fab work, that sort of thing I'm pretty confidant. 57ford/60thunderbird, when I got the set up it only had one regulator, but the front(secondary carb) had a bucnh of carbon on the inside. So I'm leaning towards two regulators.
The Carter 3721SB was one of the few O.E. Carters for which Carter published a CFM rating - 575 CFM. The 3721SB came from the factory with a primary throttle bore of 1 9/16 inches and a primary venturi of 1 1/4 inches. The Carter AFB's which were rated 400 CFM came with a throttle bore (not venturi) of 1 1/8 inches. As far as a pressure regulater is concerned: Fuel level in the bowl of the carburetor is a function of: (1) Fuel pump pressure (2) Float buoyancy (3) Fuel valve orifice (4) Float setting I have been building and using Carter AFB carburetors since 1960. I have NEVER needed a regulator. My current shop truck is a Ford 390 with 2 625 CFM Carter AFB's running an electric pump putting out 7 1/2 psi - NO regulator, NO problems. Many try to run the RACING 0.111 fuel valves on the street and have pressure problems. The 0.111's will run great at about 4K RPM UP! Two of the 3721SB's can certainly be made to work well on a 350 Chevy. These were designed to use with a manual transmission. If you have an automatic, the idle circuits may be too small, but than can be corrected. As stated earlier in this thread, slightly larger primary jets may be necessary also; but I would advise to build both carbs stock, and then tune from the base-line. If you must use a regulator, remember that the $19.95 dial-type inlines available from your FLAPS are useful if you have a strong right (or left) arm, and a rabbit problem in your garden. They may also (if clean) be successful used as paperweights. The Holley regulators (speed shop) at over $100. actually work. Jon.
Carbking, I was hoping you would chime in! I read several of your posts on this and other sites and yours made the most sense. Thanks for the response. Right now I have them soaking and have stock rebuild kits coming from the parts house. When you say primary jets, where could a person find them for purchase? Are they the same as those from Edelbrock? I'm in circle track country, so most parts places around here play with Holley's. One more question, just in case mine have already been "played with" what is the base line jets?
Master - since everything edelbrock is permanently banned from our shop, I can't answer your second question; however Carter did use more than one physical style of jet. Carter jets are readily available mail order, and probably available at a local speed shop. Incidentally, the better rebuilding kits come with primary jets, and step-up springs; parts which are commonly changed during tuning. Jon.
Cool, thanks for the info. Looks like my parts house just had the basic carb kit. So my search for jets, and springs is on.
Saw some posts of yours. You Dad was my H.S. Art teacher in Manilla, his first job. Was in Rockwell City several yeas ago. Visited good part of a day.
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