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Big Block dual quad question

Discussion in 'The Hokey Ass Message Board' started by 38 Hump, Sep 11, 2012.

  1. 38 Hump
    Joined: Mar 29, 2007
    Posts: 42

    38 Hump
    Member

    Has anyone using an Offenhauser 360* low rise dual quad intake with Edelbrock 1404, 500 cfm carbs and progressive linkage experienced lean fuel delivery on the cylinders farthest from the primary carb? The spec sheet for the intake says it is specifically designed for "evenly distributed" fuel but friends have warned against using progressive linkage for just that reason (their make manifolds unknown). By the way, the engine is a mildly built Chevy 454. I have not completed the build yet and am concerned about the break in.
     
  2. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I can't speak directly to the 454 motor issue, but I have an Offy 2 x 4 intake on the 331 Ford in my 27. I am running two 600's Edelbrocks. For years I ran it with both carbs hooked up to open at the same rate, and a few years ago I redid the car and put progressive linkage on it.

    I have seen a difference in plug readings based on distance from the back carb with the new setup. But it doesn't seem to be critical as the car runs fine in all other respects.

    Don
     
  3. 38 Hump
    Joined: Mar 29, 2007
    Posts: 42

    38 Hump
    Member

    Something that I forgot to list and may factor in is, due to linkage / firewall clearance, I am using the front carb as the primary.
    Don, thanks for the info. Were the affected plugs showing any signs of running lean? I have heard that it can lean out so much that the headers glow on those cylinders.
    Larry
     
  4. 34toddster
    Joined: Mar 28, 2006
    Posts: 1,482

    34toddster
    Member
    from Missouri

    BBC isn't known for very good fuel distribution even with a single 4 BBL
     

  5. dualquads
    Joined: Apr 9, 2012
    Posts: 80

    dualquads
    Member

    im sure there must be something in the search section. i did read here a few years ago when researching the same subject for my 454 55 that i used to have, that big blocks need to have both carbs working together, if you set them up with a primary and secondary carb, the four cylinders under the secondary carb run so lean the engine actually runs a fair amount hotter...

    kev
     
  6. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Not to any significant degree that I can tell. Some plugs are just a shade whiter than others. I have noticed when I shoot my headers with the infared gun some tubes are hotter than others, but not sure of the cause.

    Don
     
  7. I run the low profile Offenhauser 2 x4 with a pair of 600 cfm Carters on a sbc . I started out with progressive and noticed leaner plugs the further from the primary carb.
    I went to straight linkage so both carbs work at the same time and all plugs are even now, I would do the straight linkage.
     
  8. jaxx
    Joined: Mar 22, 2008
    Posts: 389

    jaxx
    Member

    I must agree with dualquads from my 2/ 4s on a 440 mopar i had some years back - fuel distribution was hard tell at low rpm and the problems were so hard to identify due to the cam and low rpm roughness - we found that temps were different ( lower ) with the old drop of oil on the header trick - alot more even with both working togather and with timming setup for both togather we had less lag at take off - we were running 750 hollys though - jaxx
     
  9. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,728

    GassersGarage
    Member

    I was using the Edelbrock dual quad set-up on a 454. I ran my linkage 1:1 because I heard the front cylinders would run hot. My buddy saw it and asked why I did it. He switch his linkage and noticed the motor ran 15 degrees cooler. He has a 427. BTW, Edelbrock recommended their 600 cfm carbs for a big block, so I bought the carbs but never used them.
     
  10. 38 Hump
    Joined: Mar 29, 2007
    Posts: 42

    38 Hump
    Member

    Thank you all for relating your experiences, good information.
    Larry

     
  11. George
    Joined: Jan 1, 2005
    Posts: 7,400

    George
    Member

    With normal progressive the front bls of the rear carb would be putting mix into about the middle, running the front carb as the primary would put the mix way up front, doesn't sound like a good idea if you think about it.
     

  12. We have a winner.
     
  13. oj
    Joined: Jul 27, 2008
    Posts: 6,257

    oj
    Member

    In a pinch you can fatten the idle ckts of rearward carb to compensate fuel distribution. Personally, i ran straight linkage on my 2X4. Just giving you something to think about.
     
  14. Deuces
    Joined: Nov 3, 2009
    Posts: 19,916

    Deuces
    Member
    from Michigan

    I like Ford's idea of mounting the carbs ass backwards...
     

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