4-71 on a 300 inch Y block making 7 pounds of boost at first, then maybe up to 10 pounds. i'm looking at three options. 1. four stromberg 97's @ 150cfm each 2. two BIG stromberg 97's @ 250cfm each 3. two carter AFB's @ 400cfm each straight or progressive linkage on any of these applications? what modifications need to be made to any of these carbs in order to run them in boost applications?
I cant help with your Y block but on my flathead with a 471 Clive at Stromberg recommended three 97's with progressive linkage. Center carb choked, outside carbs have blocked chokes (the blower was actually pulling the choke blades closed at high throttle and they were getting stuck on the fast idle cam. Why don't you email Clive and tell him what you are building and have him ***ist you? you will not find a more helpful and knowledgeable guy. He is in England so pay attention to the time zones. Clive@stromberg-97.com Heck, he'll even paint them for you to match your Y block.
You have absolutely no reason to listen to me but from experience, the 4 X 150 cfm seems about right, 2 X 250 cfm seems like too little flow (especially with a blower) and 2 X 400 cfm seems like too much even with a blower. I know I sound like Goldy Locks but that is where I would put my money. For the street, I have always added 250 to 350 to the displacement of a V8 and used that number to size the cfm of the carb, but stay below the larger size calculated. In other words for a 302, I go with 550 to 650 cfm carb. I know it sounds crazy, but it has always worked. I used a 625 cfm Carter on a 302 and it was perfect. So, 300 cu in X [(14.7+7)/14.7] is about 450 equivalent cu in; 450 + 250 to 350 is 700 to 800 cfm. 500 cfm is too small, 800 would be at the absolute top unless you are planning to race it a bit, and 600 cfm may be on the light side but that is still 4 carbs feeding a plenum over a 471 which is sized for 284 cu in engine. I am sure there is someone with actual carb calculations to give you a real answer. This does not account for the artistic influence 4 carbs would look cool, dual quads looks cool, dual duals looks cool on a flathead.
Keep in mind that CFM ratings of carbs, when running multiple carbs, are not directly additive. This is especially true when comparing 2 barrels to 4 barrel carbs, the two types of carbs are rated differently. Dual 2 barrels at 250 cfm each does not equal 500 cfm, and definitely NOT the same as a 500 cfm 4 barrel carb. I don't have the formulas in front of me and I'm not going to search them out, but dual 250 cfm 2 barrels would probably equal about a single 400 cfm 4 barrel carb (after doing a little math it probably equals less than a 300 cfm four barrel carb). Dual 400 cfm 4 barrels would not flow the same cfm as a single 800 cfm carb. For the best performance I'd run the dual AFB's, but for looks I'd run the 4 97's. Either should flow enough for the engine.
BTW, here's a calculator for CFM needs of an engine: https://m.roadkillcustoms.com/calculate-size-carburetor-needed-cfm/
My choice would be the Carter 400 CFM 9400’s. They won’t be cheap but neither are the Strombergs @ $495 each. I think you can get AFB’s and rebuild them for $1000-$1200 but the problem might be finding two nice ones that are complete and somebody didn’t screw up. I would run them with direct linkage, I have two 600 Holleys on a 6-71/350 SBC and it works great direct. The 4-71 two four bbl. carb adapter is HTF but the adapter for four 97’s isn’t exactly common or cheap either.
On an open engine compartment I would run the 4x2 set up, On a closed compartment run the 2x4's with the secondaries adjusted to open late. Use the 81 carbs, smaller than the 97s. Jetting will be interesting. I just sold a 3x2 set up where the primary carb had adjustable jets.
I'd try four strombergs, and if you don't like the performance, well, it is a Y block, and you can blame it on that Whether you start with small or big ones, that's up to you. I'd go big.
I would try a single 750 double pumper. You can pick up a 4779 cheap and throw a kit in it and give it a try. A friend of mine drove a Chevy pickup for years with a 4-71 on a 327 with a 4 speed. Very responsive and good street manners.
Not going to give a recommendation, however, some information that may or may not be helpful: (1) As previously mentioned, the CFM from multiple carburetors is not normally an additive property. We normally figure about 75 percent for 2 carburetors, maybe 60 percent for 3 carburetors, and maybe 50 percent for 4 carburetors. The value of 4 carburetor is in more even cylinder fill density. (2) I have no idea what is the actual CFM for the EE-1 (a.k.a. Stromberg 97) STROMBERG DID NOT PUBLISH THIS INFORMATION! (3) Stromberg's sister company (Zenith) DID publish some CFM information in the time frame of the 97. Zenith did not publish 2 barrel data, but did publish that a single barrel size 1 1/2 (the 97 is a size 1) with a 24mm venturi flowed 120 CFM on the two-barrel scale. So using the IFF, the maximum for the Zenith 2 barrel size 1 1/2 (not published) would have been 2 times 120 or 240. Guessing this is high, as there would be some loss because of the two side-by-side barrels. But using the 240 figure, and dividing by the square root of 2 (converting to a four-barrel scale) would yield 240 / 1.414 is equal to 170 CFM maximum for the 97 (I rather doubt it is this high). The internet says 155, but does not state who, or how, but I can easily believe 155. (4) So if we use (4) 170 CFM carbs (the maximum possible) and derate them by 50 percent (paragraph 1) we have 4 times 170 divided by 2 or 340 CFM (4 barrel scale). (5) Personally, I have (2) 625 CFM Carters running solid linkage on a normally aspirated 390 bored .030 over. My own vehicle. Runs like a scalded dog. I am guessing maybe 900 CFM total, but these are Carter AFB's with the auxillary air valves on the secondary side. So total CFM is inconsequential, as the secondaries are keyed to engine demand. CFM of the primary side is the important figure. As these started life as performance Chevy carbs, they required a TON of modifications to make the Ford engine like them. (6) Have personally installed several sets of the 400 CFM Carters mentioned in this thread on 327 Chevvies with solid linkage. Everyone was very happy with the installations. (7) While Holley did not publish CFM figures on the 4000 used on the factory blower motors, comparing venturii to other carbs with published figures, they were approximately 500 CFM. The castings were basically Lincoln 368 carbs, modified for the blow-though design. I don't know the factory blower pressure. Hope the above gives you food for thought. EDIT: just read Rick's response about closed hood/open hood. It is well known that running Carter AFB carbs with an open hood will result in air velocity past the bowl vents spewing fuel on one's windshield UNLESS air cleaners are installed. Jon.
Teo Carter 425 CFM WCFB's on a 4-71 on top of a 292" SBC. Ran great on the street right off a '56 Vette.
so i'm thinking four 97's and keep the boost to 5-7 pounds and run a three V belt drive system for that period nostalgia look. i should add that the car will never see the race track, just a spirited street driven hot rod. i think i asked this question before but running 97's in a blown application, are there any specific modifications that need to be made to the carb or just use the same method as naturally aspirated applications? tight shafts and good fitting throttle plates. i think i remember DW once saying that his would **** the choke closed under load running them in enriched mode. i have four very nice large logo 97's that were made in elmira new york, so nice that they might even be n.o.s. i mean i don't want to put a screwdriver to the screws to check if they ever had gas in them. they're that nice. then again, i have two carter 9400's that were rebuilt five years ago and sat on a shelf ready to go.
I’d use a couple of Holley 2 barrels with the backs cut off like 406 Fords or 435 HP 427 Chevrolet’s used. No more than 350cfm and progressive if possible. 2 fuel lines look better than one on a blower and a 4-71 doesn’t have a lot of room on top..
The 2300 model Holley. Total cfm for two would be equal to about a single 400 cfm 4 barrel (350 x .75 = 262.5, 262.5 * 2 = 525, 525 * .75 = 393.75). Maybe a little light for that engine. But, Holley also makes a 500 cfm 2300, two of those would be equal to about a 563 cfm four barrel carb, which should be plenty for a blown 300 cu in engine.
Blues, your right about needed cfm but cruising down the hiway how much are you really using at a 1/4 throttle on both being open. Early posts talked about 400 being a great ride and performer and I was thinking that seeing 2 carbs on top of a 4-71 with a little spread between them would look good.... I’ve got 3 old Brazwell 500 AD’s that flow over 700 apiece and have unbelievable low end response power and work great on a inline 6 at Bonneville.
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