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Carter Dual 4bbl question...

Discussion in 'The Hokey Ass Message Board' started by T-Roy, Feb 2, 2009.

  1. Is there any reason an AFB and an AVS carb wouldn't work together properly? Both carbs have a rating of 400 cfm. Thanks.
  2. carbking
    Joined: Dec 20, 2008
    Posts: 2,976


    First, I am unaware of any Carter AVS that was rated less than 625 CFM.

    But even if the WOT CFM ratings were the same; it would be virtually impossible to have the spring loaded airvalve function at the same rate as the more stable weighted airvalve, as well as make the calibrations the same.

    Not saying that with much time and effort, it couldn't be made to work; but it would probably never work as well as a pair of matched carburetors.

    I personally wouldn't even attempt it. Others opinions may differ.

  3. Interesting question and I plan to pursue a similar deal down the road by mixing a lean jetted 600 cfm smog Holley carb with a Carter (Edelbrock twin) 500 cfm and - for the first time ever - run progressive linkage.

    Another interesting one would be to run a 750 Carter in front with a 500 CFM Carter in the back and again, progressive linkage.

    Since both carbs dump into a common plenum I don't think there would be a problem.

    Guessing too that jetting could be considerably leaner - within reason - on the primary carb.

    I believe it was Stu Hilborn who ran three 1-bbls and one 2-bbl on each corner of a home-made intake on a dry lakes flathead.

    Fwiw - the 500 cfm Carters on my 462" Buicks dual quad setup seems to have the air valves opening at slightly different times.
    Tip-in on the secondaries is very smooth . . . running straight linkage here.

    Not at all like the single 600 cfm smog Holley with vacuum secondaries that kick in with a lunge sorta reminiscent of 'turning on the 2nd engine....'
  4. Thank you Jon. That's the info I was looking for. I'll keep looking for a pair of 400 cfm AFB's.

  5. C9, I had thought of using a 500 AFB along with the 625 AFB I have now, but my motor won't need that much carb.
  6. My understanding is that the carbs you have are self-limiting in the airflow dept.

    Meaning that the air valve opens only as far as the engine's air flow capabilities will allow.

    A 500 cfm carbs airflow is more of a basic indicator of capacity than anything else.
    It will flow more than its rating if it's installed on a big engine that can draw a lot of air.

    If you have a couple of carbs that'll fit and are in good shape, go ahead and run them until you can get the carbs you want.
  7. George
    Joined: Jan 1, 2005
    Posts: 7,379


    At 1 point Carter made matched pairs of 400s for 2X4 set ups.
  8. panic
    Joined: Jan 3, 2004
    Posts: 1,450


    Buicks dual quad setup seems to have the air valves opening at slightly different times

    Not surprised - the front secondarys between the 3-4 pair and 5-6 pair, and the rear secondary is right at the 7-8.
  9. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,103


    helped a friend with a similar setup--orig. 57 Vette intake with two 500 CFM Edelbrocks with adapters--straight linkage and a pretty strong 327 (Bullit cam and valve train, 10.5/1 comp. and big heads) it runs very well on the street and is quick too. Putting together another set now with old Carters for another 327-take some sorting out but his have been on the street now for 3 years with no issues and some long road trips as well.
  10. I'm in the middle of pulling out / tearing down my motor (355) for a rebuild. When it goes back together, it'll have @ 9.5:1 static, a Comp hyd 270 roller, Edelbrock 2x4 C26 manifold, ported 041 heads, Thorley headers, TH350 trans, 2100 stall converter and 3.50 gears in my 57 wagon. I think a set of early 400 AFB's would work pretty good, and fit the look I'm after. Would also like to find a couple of Cal Custom carb scoops for the carbs when I find them.
  11. carbking
    Joined: Dec 20, 2008
    Posts: 2,976


    Troy, the part numbers for the original Carter 400's are 9400s and 9410s. They may be used interchangeably, as the difference is an EGR port which may be capped on the 9410s.

    We have used the 400 CFM successfully on stock 350's; but a 350 with a roller cam could use more carburetor than the 400's.

    Carter made the 500 CFM as part numbers 9500s and 9510s with electric choke (run both simultaneously); or the old comp series 4758s (manual choke), 4761s (chokeless) to run as a primary/secondary setup.

    The 625 CFM would be 9625s or 9635s (NOT the 9635sa) for electic choke; or 4759s comp series manual choke.

    I would stay with genuine Carters, rather than waste time with the newer clones. My professional opinion, others may differ.

    For comparison, I run 2 of the 4759s 625's which I have modified on my Ford shop truck with 390 CID engine. I use solid linkage (both carbs work simultaneously), and it runs like a scalded dog! Good fuel mileage also.

  12. carbking
    Joined: Dec 20, 2008
    Posts: 2,976


    C9 - the different size carbs might work for you, but probably less well than a pair of matched carbs. Consider the following:

    The fuel/air flow in any manifold is never exactly equal. Most remember how well the mighty Chrysler hemi would run back in the late 1960's. This was mostly attributed to the hemispherical head design (which Chrysler did NOT invent, but that is another story); but I would suggest a lot of the performance was due to the abundance of Chrysler engineers (remember the old ad from the early 1960's "Chrysler employees 1100 engineers and 9 designers" [​IMG] ).

    In any event, the Chrysler engineers went to great lengths to understand and correct for manifold flow. The following is jetting calibrations for the factory dual quad Carter 750 CFM carburetors 4345s (front), and 4346s (rear).

    Values are given in drivers side and passenger side for those who drive in the USA. For those of you who live in areas where you drive on the wrong [​IMG] side of the road, simply reverse the numbers.

    Front carb metering areas in square inches:

    Primary drivers side 4.18E-3
    Primary passenger side 3.84E-3
    Secondary drivers side 4.66E-3
    Secondary passenger side 5.41E-3

    Rear carb metering areas in square inches:

    Primary drivers side 6.42E-3
    Primary passenger side 6.42E-3
    Secondary drivers side 4.30E-3
    Secondary passenger side 3.32E-3

    For those unfamiliar with the E terminology, E-3 means to move the decimal 3 places to the left; thus 4.18E-3 could be written 0.00418.

    Note that the only two calibrations that are the same in the square 750 CFM dual quads are the primary calibrations on the rear carb.

  13. I'm running a pair of Carter 600's on a mid range 350 and it runs great, the only problem I have is off a dead stomp it bogs a bit. If I run the rpms up to a grand then floor it, it takes right off.
  14. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones

    I think a set of early 400 AFB's would work pretty good, and fit the look I'm after. Would also like to find a couple of Cal Custom carb scoops for the carbs when I find them.[/QUOTE]

    Basically, that is what I'm running, except my old Cal Customs aren't the scoop type. I've been running this for about three months on a new .60 over 283 and have no complaints. Runs well and I love how it looks.

    Attached Files:

  15. Speedy, that's the look I'm after... Bitchin'.
  16. 39delux
    Joined: Nov 1, 2002
    Posts: 331


    That's a nice looking setup. Too bad you can't set the wayback machine to the '60s when J. C. Whitney would sell you a brand new matched pair of 409 AFBs on the brand of intake of your choice for a little over a hundred bucks.

  17. After too much thinking and a lot of reading, I've now got another Carter 600 AFB on it's way to my house to match the one I already have. Thank you to everyone who posted. I'll of course post pics and a review of how the car runs once I get my motor torn down and rebuilt.

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