Wonderin and worryin ahead on my Roadster....Its a stock 409 Chevy with 348 tripower manifold.I know run all three or be a whimp.....YOU DO IT-I AINT STUPID! I have had many 3x2's and dual fours over the years and Im thru PUNISHING my self with a hot rod that runs like a peice O **** in traffic and only runs when wide open. I was wondering what carb would have the biggest CFM rating that would still bolt up to the small base pattern of the 348's manifold. I have three brand new two barrels from ebay . One is from a TRUCK[maybe a 2 ton?] and still bolts up-the other two are from -#1 ,a 307 chevy and #2- an Olds of some variety! I think Ill just use one of the new ones and clean up two deadbeats I have to finish the trio........ does anyone know of any specific carb that would be best for the single operating carburetor,[sizewise]? Would re jetting do it enough good- even if the ****erflies are close to same?
Years ago, I discovered that Chevy's 400 small blocks had a larger Rochester 2v carb than their 305, 307 and 327 cousins did. I had a few 400 two barrel intakes and carbs, and dropped them onto a couple of "smaller small blocks"...sold one to a buddy with a 283 and he said it made a noticeable improvement! Also, if ya wanna be real sneaky about it, grab a roundy-round magazine off the rack somewhere over in Macon and look through the ads. Alot of racing cl***es require a single two barrel, and there are carb builders selling tricked out Rochester 2v carbs that flow up to 950cfm! Run a gnarly carb like that in the center with two dummies, and you'll get all the flow of three carbs without the multiple carb issues you DON'T want to mess with! (It'd look cool, and still run like a Mutha!!! ) But, on the cheap...I'd look for a carb off of a 400 small block. Probably get one free from someone if ya catch 'em before they throw it out in their hurry to dump on a 4v! (Don't know their exact cfm rating, but you can physically see that the throttle plates are larger than the ones on the carbs off of smaller engines.) If I still had any, I'd send 'em to ya!
Yeah Greg- I was thinkin about those....them and some 350 truck carbs are definitely bigger CFM and JET wise... Problem is they also share a bigger mount bolt circle than the 348 Intake along with bigger venturi bores....... Seems Im stuck with the small base as for ease of install and the time factor[reality]........
Know anybody with a Bridgeport mill? If so take the manifold and large carb to him and turn him loose. Plug the small bolt pattern mounting holes, redrill the larger pattern, and open up the throttle bores to match the larger carb. Should be a piece of cake for anyone with machine shop experience. While your at it have him do the end ones also then you can run three of the big Pontiac or Olds 2bbl carbs. Make that 409 act the part. Frank
Forgot about the bolt pattern being different...the throttle bores would be easy to hog out with a die grinder or something...e****ially if the intake is aluminum. I'd see where the mounting holes fall just for fun...if there is enough "meat" around where they need to be, a drill press and a tap could do the job for ya in a pinch...I've drilled and tapped aluminum intakes and adapters before to put oddball carbs on 'em! Also, I'd still look into the guys that do carbs for roundy-round cars...odds are they can do up one of the physically smaller 2v carbs to give you a sneaky "bolt on" performance carb! In a car as light as yours...a "two barrel" 409 should really rock & roll for ya!
The bigger center carb wouldn't clear the other two in the bolt spacing arrangement......After 35 years of ****in with this stuff Ive learned not to care what anybody thinks of my cars-I just do em nowadays to suit my purpose and enjoy em-not torture myself with self imposed trouble. Ill find out soon enough how it runs and will report back ...... I am making some progress on it..I have the front end/radius rods installed WITH steering-and all the brake lines and Master cylinder mounted and am mounting the 9" rear this weekend....my goal is to have ch***is rolling and painted including motor and trans in it also........this week.
If you're going to go through all that trouble, just stick on a big 1x4 onto an aluminum intake. After all... you don't care what anyone else thinks, right? Personally, I think the 3x2 setup I have is a piece of cake and I've only had trouble with it twice in 6 years: The float sank in the middle carb (popped off top, stuck in new one, put it back on... done.) The second one was I had varnish stuck on the throttle shaft on the front and back carbs. So that necessated a rebuild of all 3 carbs. I wasn't getting on the 348 like I should... So... now every time I get on the freeway, I floor it and run all 3 carbs. No problem. Travis
Im runnin the 348 intake cause I like the look on an open engine bay-Thanks for the tip Travis- next time those three carbs puke in traffic,you think of me..... ha!
According to the charts, the 350 SBC shares a Rochester 2-bbl with the 400 SBC from '70 through '74. The numbers are the same across the board, differring only by year which probably has something to do with EPA jetting/adjustment differences.
Thanks AV8...I believe that he 70 was the first of the larger overall sized carbs that are not the small base pattern. I am thinking now that the 69 truck carb with a re-jet may be the best I can do on short notice and maybe something more exotic at a later time....thanks.
Chop, I posted this Rochester info the other day for Marq. But here's the info for you just the same. Here ya go. Rochester 2G 11/4 flange 17/16 throttle bore 13/32 venturi 278 CFM Rochester 2G 11/2 Flange 1 11/16 throttle bore 13/16 venturi 352CFM 11/4 venturi 381CFM 15/16" venturi 423CFM 13/8" venturi 435CFM this is directly from the book Rochester Carburetors by HP Books Carburetors are tested at a given pressure drop at WOT to obtain cfm rateing indicative to flow capacity. One- and two barrel carburetors are tested at 3.0-in.Hg pressure drop. Four barrel carburetors are tested at 1.5-in. Hg drop. To compare the two rateings, use these equations: Equlivlent flow CFM at 3.0 in. Hg = ----------------- At 1.5 in. HG 1.414 Equilivelent flow = CFM at 1.5 in. Hg x 1.414 At 3.0 in. Hg So a 2G that is rated @ 278 would be the equilivelent to a 4 bbl that is rated @ 196.6 <font color="red">Rochester 2G 11/4 flange 17/16 throttle bore 13/32 venturi 278 CFM </font> I'm runnin' 3 of these on the 383 in the Chrysler. Progressive of course. Just so you don't have to go by make and model you can just measure what you got.
Thanks Ben.....I have got the carbs I have out and took pics...seems the Olds one is slightly off on the base bolt pattern[bigger]and has a FRONT fuel inlet as opposed to side on the chevys.. But the good news is I have an almost perect matched pair of 1-7/16"...[283 V8-chevy carbs] and that would be 556 CFM as the pair-I think. If I were to try to add a third matching one which I dont have- it would amount to 834CFM I might try the TWO-one in front and one at rear running simulaneously and see how it acts....... Guess I could try running them on either side of a phony center carb SIMULTANEOUSLY.
I run a matched set of carbs from a 1960 348 on my Ford 302. End carbs do not have idle circuts or provisions for chokes. Also note that no two carbs have the same pump shot rods. All of this is factory GM stuff. You adjust the pump shot by bending the rods so the end carbs come in at the same time. My setup runs hard.
I've learn't something here, I have a 2bbl Rochester in on the 283 in my A truck, I got it from a 3/4 tonner and I would say its a bit rich on the little chev, I used it for good gas miles and its not as good as I thought. I will have to look for a 305 2bbl. Is there any casting #'s i should look for so I get the right one???? Thanks, Kerry, England.
The largest cfm Rochester 2 jet carbs that i could ever find were on the late 60 through 70's Pontiac 455 ci.2V engines. The Olds 455's i found were smaller venturi size but mayby some Olds or Caddys might have had the same as the Pont 455 Good Luck
I run 3 2 barrels on a edelbrock intake on e 350 smallblock daily,the carbs are the small bore ones of of a 283,the outer carbs have the idle screws turned all the way in ,the linkage is progressive,so the middle carb opens all the way,then the 2 others start to open. it runs hard and fast ,with a 4 speed and a 373 posi,i don't know what kind of problems y'all are talkin about, as i've never had any with my setup, and i drive it daily.well goood luck with er
All good information- Thanks....I think the difference is that I am gonna run tall 16"s with a 3.0 rear gear and a stock auto ****** and stock stall convertor. Thats why I was wanting to stay with one or two carbs rather than all three. you are SURELY about IDEAL with the taller3:73 gear and the 4 speed setup for sure.........
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