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Technical Has anybody adapted a 4 bolt Stromberg to a 3 bolt stromberg manifold on a Buick straight 8?

Discussion in 'Traditional Hot Rods' started by strait8, Jan 20, 2017.

  1. strait8
    Joined: Jun 11, 2014
    Posts: 142

    strait8
    Member
    from Skokie, IL

    I have a dual carb manifold from a 41' Buick that I would like to utilize. It is the correct size for my 263. I have two 1951 straight eight 263's that both came with the 4 bolt style Stromberg. The challenge is that I would like to use the 4 bolt carbs I have on this manifold if it is not too hard to adapt. I've seen adaptors that look like they would work. Most of the adaptors seem like they are made to go from a Stromberg to a Holley or vice versa. I have not seen Stromberg to Stromberg. My research shows that the original rear carb had no choke and sat on some sort of a spacer to get it up to the same level as the front carb since the engine slopes down. Not sure if this "leveling" is necessary either. I want to use the carbs simultaneously unlike the way the 41's that worked "progressively" I believe? Has anyone done it? Multiple carb gurus please let me know your thoughts!
     
  2. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    The spacer was an air flow valve rather like what is used in some four barrel carbs...it was just a spring-loaded flap that prevented air from going through the (no idle circuit) rear carb until there was enough flow to put its venturiis to work. I think all the carbs you are discussing are AA Strombergs...see if the front 2 bolt holes line up the same for 3 and 4 bolt ones, if so you can likely do something with a drill and a tap. Think about using 2 primary carbs with straight linkage, getting rid of some of the trouble...
     
  3. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,355

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    Here is what I did. I have a '38 Buick with a single 2 bbl Stromberg that did not function well.
    It had the 3 bolt base and would not accept the 4 bolt carb from my '53 263. However, I also had
    on hand an NOS reman Rochester 2GC from a '66 era 300 cube Buick V8. I also had one of those aluminum 3 bolt to 4 bolt adapters that can be used on flathead Fords to use 4 bolt carbs.

    The 3 bolt pattern of the adapter is the same as my Buick manifold and the 4 bolt matched the 2GC.
    This particular model 2GC had a water heated choke element and I did not want to use that because the plumbing would not be neat and tidy. So, I used a manual choke conversion on the carb and used the '38s Throttle cable to operate the choke. (the '38 had a form of automatic choke).

    However, I was concerned that the adapter became, in effect, a small plenum and eliminated the separation of carb barrels that existed in the stock setup. So, I fabbed an insert for that adapter keeping the original arrangement of one barrel feeding each branch of the manifold, which are separate, each feeding 4 cylinders.

    I can't say I know for sure that was important, but it did work very well and the 2GC provides easy starting, smooth idle and acceleration.

    I, too, have a dual intake manifold from a '41 248 and a 263 they may be used on. If I go that route, I intend to use two carb adapters in a similar fashion on the 263. What I don't know as I sit here typing this...is if the the Stromberg 4 bolt pattern is the same dimensions as the small base Rochester...I never tried it.
    . IMG_0449.JPG IMG_0452.JPG IMG_0450.JPG IMG_0451.JPG IMG_0453.JPG

    Ray
     
    Last edited: Jan 20, 2017
    LONG likes this.
  4. LONG
    Joined: Aug 20, 2011
    Posts: 292

    LONG
    Member

    I have a dual manifold too. 3 bolt. I have a couple 4 bolt carters and couple strombergs. I think they are all different sizes. too poor to install right now. I bought a core 2gc this fall and it has the same 4 bolt pattern as buick. there is a large bore and small bore 2gc.
     

  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,802

    jimmy six
    ALLIANCE MEMBER

    I bought 2 piece adapters off e-bay that worked perfect. They looked like risers and showed well.
     
  6. carbking
    Joined: Dec 20, 2008
    Posts: 3,715

    carbking
    Member

    Stromberg produced 2-barrel carburetors in THREE different 4-bolt flange configurations; plus the 3-bolt configuration.

    Always bad to generalize on "will it fit", when measuring devices are readily available.

    As mentioned by Bruce, the "spacer" is actually an auxiliary air valve, which (when not warped as they normally are) opens on engine demand if the carburetor throttle plates are also open. Unless the valve has been reworked, one's chances of finding an original that is still functional are less than one's chances of winning an argument with the IRS ;)

    If using straight linkage, the air valve is not only not needed, it is not wanted, and should not be used.

    While many seem to look only at "will it fit", a better question is: "will it fit AND work?". The Strombergs came in several different internal venturii sizes. For best results, two carbs running straight linkage SHOULD be identical by identification number AND the internal venturii should be sized to the air requirements of the engine (see the second line in my "signature"). Remember the "six P's of engineering".

    Jon.
     
    302GMC and LONG like this.
  7. strait8
    Joined: Jun 11, 2014
    Posts: 142

    strait8
    Member
    from Skokie, IL

    Sorry guys...I work weekends and did not get a chance to see the responses. Wow! Thank You!
    I did a little measuring and unfortunately the spacing on the front two bolts are 3-1/8" on the dual carb manifold and 3-1/4" on the two carbs that I have. I checked the series of the two carbs I have and they are identical. 7-90B. Looking at both airhorns there is a number stamped on both of them both have 1-3. Not sure what that means but they are the same. On the rear of the carb there are identical stampings of 1-1/32. That appears to refer to the venturi sizing in the manual. I have a third carb that has different numbers. 7-88B and 1-2 on the air horn with the same 1-1/32 stamping on it. Bolt holes are the same spacing. Luckily it seems I have two identical carbs. The question still remains if there is a spacer that gets me from one bolt pattern to the next. Does anyone know if the spacing for the 3-4 hole adapter for the rochesters happens to be the same as the Stromberg 3-1/4". Jimmy Six what did you use? If so sounds like the adapters will allow me to bolt em up but I still have the issue of the carbs sitting at different height. If it is an issue? I understand that for the rear carb on the stock setup that it was used as an auxillary and can be omitted but does the height play a part in fuel distribution? Carbking talks about air requirements of the engine. My engine is stock so no added requirements. I am guessing the refers to cfm? I have looked to see what the cfm is on these carbs in my manual but there is no mention of them or what the engine requirements are. I am guessing there is an equation for such a thing and changes to the carbs as far as jetting may need to happen since I will be using two of them. How do I figure out what I need? Carbking....are you suggesting I scrap my idea of these carbs since I need to modify too much? Hnstry...I love the fabricated part you made. Looks great and seems it should do its job. Does anyone know if it is necessary? Sorry if I am "green" with regard to the whole multi-carb thing but...well.....I am! By the way did I say you guys are awesome! I love this S#!t and being able to have nice people like you all to bounce ideas around with. Your knowledge, experience, and patience is incredible.
     
    LONG likes this.
  8. LONG
    Joined: Aug 20, 2011
    Posts: 292

    LONG
    Member

    these folks? http://vintagespeed.com/ I contacted them 4 or 5 years ago wanting a 4 bolt flange to dual. their response "I MAKE AN ADAPTER TO MOUNT TWO 3 BOLT 94 OR 97 CARBS TO YOUR WCFB INTAKE. CHECK PART NUMBER FL-CA-5 IN OUR ON-LINE CATALOG" so I would think they have something that does fit.
     
  9. carbking
    Joined: Dec 20, 2008
    Posts: 3,715

    carbking
    Member

    "Carbking....are you suggesting I scrap my idea of these carbs since I need to modify too much?"

    No, not at all. What you have will work, although something somewhat smaller would work better. You may (or may not) have to install richer jets (both idle and main metering, the discharge jets should be fine) as too large a carburetor (in this case 2) will run lean.

    If you had asked what to use, I would have suggested carbs from a 1946~1950 Buick 248 rather than the 1951 Buick 263, but you will be able to tune them, just less easily than the smaller carbs.

    As to your comment concerning CFM, there have been several billion (at least) pixels disturbed on the internet discussing CFM. Here is a link to several of those disturbed pixels: http://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

    As far as the equation you mentioned, there are several in use; here is a link to probably the oldest, and the one I use for street carburetors: http://www.thecarburetorshop.com/Carburetorsizeselection.htm

    And one more link; I realize you do not have a 4 or 6 cylinder like the link, but the general criteria are the same: http://www.thecarburetorshop.com/Dual1barrelcarbs.htm

    Jon
     
    Last edited: Jan 24, 2017
    LONG and Rex_A_Lott like this.
  10. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    I vote for the Rochester great carbs just remember there are small and large bolt pattern ones. You are wanting the small pattern.
     
    Hnstray likes this.
  11. Jenz38
    Joined: Dec 21, 2010
    Posts: 81

    Jenz38
    Member

    I run the same constellation ,a 263 with the compound carburetion..,run also two single carb AA- Strombergs similar on it..
    Runs very amazing .... ,the only little "problem" are, the two idling systems...so the engine idle at 800 ,less isn't possible without completely closed (sticky) flappers.
     

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