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Projects Toploaders.3spd vs 4spd in a Buick

Discussion in 'The Hokey Ass Message Board' started by Donuts & Peelouts, Dec 4, 2017.

  1. II FUNNY
    Joined: Jul 31, 2010
    Posts: 1,785

    II FUNNY
    Member

    They came on some Buick’s and some Pontiacs. They are just an 850cfm version and look the same as a 750 from the outside. If you compare them side by side the area under the secondary air valve is bigger. There’s certain part numbers to look for that you can get by googling it. I don’t believe any Chevy or olds came with an 850. Ford also used a quadrajet on a 428 super cobra jet I believe. Not sure what size though. I guess technically they’re rated at 800cfm. Edelbrock called them 850’s


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    Last edited: Dec 6, 2017 at 10:09 PM
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  2. All 1.21 venturi Qjets are 800's, even the E-brock "850". They just opened the top flapper a bit farther.
    All 1.09's are 750's , except the 72 Pontiac 455 HO, which was cast without the outer booster ring on the primary side..Sometimes called 800's, also.
    All secondary bowl castings are the same..E-brock and all.
     
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  3. carbking
    Joined: Dec 20, 2008
    Posts: 2,029

    carbking
    Member

    The 1971 H.O. and R.A. Pontiacs with the single booster are called 850's. Very scarce, very expensive.

    7041267, 7041268, 7041270, 7041273.

    Some of the service replacement 7041263 also have the single booster.

    As far as I am aware, these are the only ones.

    EDIT: These have been in demand for years, and there are a few "less than honest" individuals who have restamped 750's with the above numbers for the numbers-matching crowd. Very easy to spot a restamp of these by looking at the booster. Also, if the price is too cheap, run, you did NOT find one that someone didn't know the value. ;)

    Jon.
     
    Last edited: Dec 7, 2017 at 6:49 AM
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  4. Jon, Those are called 800's in the racing community.
    They were all 1.09 venturi. It seems unlikely that the missing outer ring would add 100 cfm.
    Who knows what they're called on the internet or at the local cruise night.
     
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  5. carbking
    Joined: Dec 20, 2008
    Posts: 2,029

    carbking
    Member

    Mark, actually, they have been flowed by some of the Pontiac enthusiasts, and do outflow the 800's.

    And the racers are the ones that "ruined" the going prices some 40 years ago!

    Jon.
     
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  6. carbking
    Joined: Dec 20, 2008
    Posts: 2,029

    carbking
    Member

    A bit more information on the spread-bore carbs:

    Rochester designed the spread-bore, and it came out on 1965 Chevrolet. Rochester sublet some production to Carter. As more production vehicles converted to the spread-bore in 1966, Carter continued to build, under license to GM, Quadra-jet carbs. Regardless of what pixels you may have seen disturbed on the 'net, these were essentially the same carb as their Rochester counterparts. Rochester supplied, tooling, metal, engineering, etc. Carter supplied production line capacity. Over the years, Carter built literally millions of original equipment Q-Jets. All of the O.E. Carters carry the Rochester part numbers.

    By 1968, with GM approval (isn't is nice when companies actually work together), Carter was offering aftermarket replacement Q-Jets with Carter part numbers (4 digits, followed by the letter "S" as in Sam) as opposed to the normal 7 digit (sometimes 5 with the "70" omitted) Rochester number.

    In 1969, Carter released their spread-bore, the thermoquad or TQ, again, no issues from GM about using the spread-bore design. The TQ's released were designed for racing, and were rated 850 and 1000 CFM; with the major difference (there are others) being the 1000 had the idle booster removed. These were hugely successful with the racing community; so much so that Chrysler had a detuned version in an 800 produced for the 1971 340.

    In 1971, with Carter's approval (again, nice to see companies work together), Rochester brought out the single ring booster for use with performance Pontiacs. This was a one-year only application.

    Rochester was using some 800 CFM (larger venturi) on larger engines, but most were the 750 (smaller venturi).

    Carter, on the other hand, was producing 800 and 850 carbs for Chrysler. Also 800 CFM for Lincoln, and performance SBF (export only). It was found that the transition from primary to secondary was smoother, even on the smaller engines using the 800 (essentially 200 primary - 600 secondary) rather than the 750 (essentially 150 primary - 600 secondary); so by I think 1976 Rochester started using 800's on everything.

    Holley and Autolite also had spread-bores, but neither have a good reputation with performance (although there are bound to be a few who are happy with these), and I know little about either the Holley spread-bore or Autolite spread-bore.

    And a performance note: neither the Carter 1000 or the Rochester 850 idled WELL on the street. Both do have idle mixture screws, but the absence of the idle booster slows the idle air velocity. Yes, they would idle, just less smooth than carbs with an idle booster.

    Jon.
     
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  7. Ha..Don't really doubt that, but some of the guys would have enough sense to not brag too much about a carb that's supposed to be a 750 from the factory.;)
    Now, are you sure it wasn't the numbers matching GTO crowd that drove up the prices?
    You know, the one who won't go anywhere near a dragstrip, that are afraid they might hurt their investment? LOL
     
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  8. carbking
    Joined: Dec 20, 2008
    Posts: 2,029

    carbking
    Member

    Mark - there is certainly some of that, but the racers are the ones really responsible.

    Since the Rochester changed from the 750 to the 800 as the standard, prices of the 1970 Buick Stage carburetor (early 800) and the 1973 and 1974 SD Pontiacs (also 800) have dropped by two-thirds. Why? no longer the carb to have by the racers.

    Another excellent example is the center carb on the 1966 Pontiac tripower (very rare, very expensive). For years, it was the "darling" of the dirt track roundy roundy racers that had to run a "stock" ;) two-barrel.

    Jon.
     
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  9. wicarnut
    Joined: Oct 29, 2009
    Posts: 1,751

    wicarnut
    Member

    If you decide on shifter route, buy a scatter shield, a must IMO. ( Note, banging gears is fun,Been There, Done That ! But breaks things on a regular basis compared to an autotranz, again IMO) Being your first build, I would recommend a TH400 w/ mild shift kit, 3:25 gears or 3:55. That BB Buick stock will melt the tires off, recommend not getting to radical so car is enjoyable for cruising and occasional fun. This advice and $2/3 will get you coffee most places I hang out. Have Fun, Be Safe and Have At It !
     
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