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Technical Running carbs backward?

Discussion in 'Traditional Hot Rods' started by judgeyoung, Nov 1, 2013.

  1. judgeyoung
    Joined: May 21, 2010
    Posts: 141


    I am designing an intake to run 6 Holley 94's. It would work better clearance-wise, fuel line-wise and linkage-wise if I run three (one bank) reversed from the normal direction. What problems could I run into? Slosh uncovering jets? Fuel distribution? Vents? Or?????
  2. Well Ford ran their factory 6 barrel setups for the 390/406 backwards. I would think if the factory thought it would be ok then it must be.
  3. Straightpipes
    Joined: Jan 25, 2006
    Posts: 1,084


    The carb don't know which way it's facing...........
  4. judgeyoung
    Joined: May 21, 2010
    Posts: 141


    Well, early 94's aren't exactly 2300's like the backwards factory setup uses, and your carb may not know which way it's facing, but unless you routinely do your burnouts in reverse, I'm bettin it DOES know which way it's facing during launches! :)

  5. The carb doesn't know or care that is until acceleration forces all the fuel to the rear of the car and back )front( wall of the fuel bowl. it depends on the design of the carb but you could wind up in big trouble.

    That's why he's asking and I wish I had the answer
  6. I Drag
    Joined: Apr 11, 2007
    Posts: 884

    I Drag

    I was once contemplating putting a holley on backwards to simplify the linkage. I called Holley directly and talked to a technician about this. He said that this is sometimes done and that the carb would run the same.
  7. propwash
    Joined: Jul 25, 2005
    Posts: 3,858

    from Las Vegas

    Even Ford's beautiful dual quads were mounted "backwards". Never caused a problem for me, and these FEs do know how to accelerate. Stop and think about the way some tunnel ram setups are oriented sideway. Never seems to cause a problem.
  8. Model T1
    Joined: May 11, 2012
    Posts: 3,309

    Model T1

    That was my first impulse answer. But I'm not sure either. I agree, it depends how hard you tromp on it.
    I ran 2-4's in an Austin Healey Sprite with 327 SBC and it would load up on hard turns. Switched to 3-2's on Offenhouser and it ran fine. Okay nothing to do with backass words carbs but maybe similar problems could come up.
  9. blackrat40
    Joined: Apr 19, 2006
    Posts: 1,167


    What kind of carbs were on the 3-2 setup?
    I have a 3-2 setup with Rochester 2G's that I am thinking about trying
    backwards for several reasons. It's not a all out drag car so I am thinking
    it will work OK. Maybe a little stumble with a "neck-snapping" launch.

    Attached Files:

  10. tubman
    Joined: May 16, 2007
    Posts: 5,201


    I have a small base 2GC on my '51 Ford. Everything lined up better that way. Works fine.:)
  11. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606


    Here's my speculation:

    Two things might cause erratic carb function under hard acceleration:-
    1- Raw fuel could slosh out of the bowl vent and down the carb throat, resulting in an overly rich condition. Jets and various passages are too small to allow significant sloshing.
    2- If the float pivot is ahead of the float, fuel packed up against the back wall of the float bowl might keep the float high and the inlet needle closed too long, resulting in low fuel level in the bowl and a potential lean condition.

    I think if you rotate the Holley 94, the vent orientation would make slosh less likely, and the float/ pivot arrangement would make the float more likely to drop, allowing the float bowl to fill, or possibly overfill slightly?

    Maybe I'm overthinking this? Bottom line, I'll bet it'll work just fine.
  12. It depends on which model 94 you are using...
    The accelerator pump well inlet hole in the bowl on some has a short wall around it
    and it may run dry under hard acceleration. As long as you drive "normally" and your float level is set correctly you should have no running problems reversing one set, though linkage may be a problem.
  13. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,291

    Rusty O'Toole

    Throttle arms will be on the wrong side and work backward (push instead of pull).
  14. aircap
    Joined: Mar 10, 2011
    Posts: 1,547


  15. dickster27
    Joined: Feb 28, 2004
    Posts: 3,137

    from Texas

    I can guarantee you if you use first generation 94's you will flood out the carb every time you hit the brakes because the spray bar rears are lower than the bowl wall. But 2nd and 3rd generation 94's will work fine turned rearward.
  16. The only concern would be leaning out of the mixture going up hills,this is why they are the way they are. JW
  17. Tim_with_a_T
    Joined: Apr 30, 2011
    Posts: 1,013


    I don't think linkage would be easier to fabricate if 3 carbs were forward and 3 backward. You'd have one side pulling and the other pushing. I'm not saying it would be impossible, but it would certainly be easier to have them all open the same direction. Think about fuel line fabrication, too. You'd have them going opposite directions.
    You may encounter fuel sloshing and fuel starvation as others have mentioned. I think that would be something you'd just have to try out to know for sure. One thing that's cool about Holley 94's is their main jets are the same as Holley 4bbls. could run jet extensions like they sell in Summit for the rear float bowls of a double pumper. That would eliminate the potential starvation at least.
    Since you'd be designing the manifold anyway, why don't you drill/tap the carburetor mounting pads so that you could mount them either direction? That way if backward mounting sucks, you can just flip them around. I guess you could do this as a post-machining operation as well (like later on down the road).
  18. carbking
    Joined: Dec 20, 2008
    Posts: 2,866


    Why not simply machine an adapter to turn ONE around on your current setup, and try it?

  19. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    American Motors mounted 2 barrels sideways on their 6 cylinders and they would die out on a hard turn in one direction.
  20. badshifter
    Joined: Apr 28, 2006
    Posts: 3,224


    8 million V Drive boats say the carbs will be fine backwards.
  21. KB1shortbed
    Joined: Nov 2, 2013
    Posts: 1

    from Buda Texas

    Ford wasn't ALL wrong.
  22. As long as the jets stay covered with fuel, your good to go.
  23. judgeyoung
    Joined: May 21, 2010
    Posts: 141


    Thanks for all the input. I know there is no problems with later model Holley 4 barrels. I've run them sideways and backwards, but these old 94's have some issues that newer designs don't have.

    I am building an adapter to run 6X2 94's on a single four barrel intake. I am trying to design it so that each of the manifold's holley flange bolts goes through the single bolt end of the three-bolt flange of the 94's. I am using 1.5"X 3" rectangle for each side's plenum and they will be about 1.5" apart. Sorry it is so hard to describe.

    If I turn one side around, they center on the manifold better, leave room for the linkage on the outsides, and all of the fuel inlets align to the inside so I can just drill a piece of pipe for a fuel log that should look cool. The reverse bank also gives a nice slight offset for that side set of the carbs that just looks better.

    I am going to run a shaft across the back of the carbs with one linkage pointed up and the other down so they will operate the throttles the right way. I am also using those levers to build my progressive linkage. I am even contemplating having a three phase progression, running on two carbs directly, then bringing in the second set, and finally adding the third pair. I know the adapter will not be terribly efficient, but should not be too bad due to the carbs being pretty close to the original opening and the small plenum volume.

    I am using a single plane first, but may possibly use a dual plane and separate each side plenums so 3 carbs feed each side with only a balance tube between. We'll see...
  24. JakeDW
    Joined: Sep 30, 2012
    Posts: 580

    from Missouri

    Come on those don't launch hard LMAO.(sarcasm)

  25. judgeyoung
    Joined: May 21, 2010
    Posts: 141


    Anyone ever seen 94's run sideways on a manifold? I don't think it would be much of an advantage, and, of course, linkage would be a nightmare, but I don't think I've seen it on a V/8. May have on a 6. Might let them fit closer together, though. Wonder how g-forces would affect them that way.
  26. speedshifter
    Joined: Mar 3, 2008
    Posts: 226


    Regarding 56Don's post about Ford 390-406 3x2 factory setup. The carbs were backwards. They caused problems when braking hard at high speeds. Raw fuel would slosh out of the bowl vents & go directly down the venturis, flooding the engine. I cured this on my 406 dirt track racer by lowering the float levels below factory specs.
  27. gibraltar72
    Joined: Jan 21, 2011
    Posts: 260

    from Osseo Mi.

    Tried mounting a 2CG backwards on an engine in an old modified stock car years ago because linkage was easy to hook up. Car would come off turn like gangbusters but just quit about half way down chute. Couldn't figure out what was going on. An oldtimer looked at it and told me to take extra time to make needed linkage cause it was starving on acceleration Took his advice and car ran all the way into turns instead of falling on it's nose in middle of straightaway.
  28. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    from BC

    Or you could just stick a 90 deg. plug boot on the vent tube...
  29. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907


    I'm with the carbs don't care which way they face !

  30. fordflambe
    Joined: Apr 9, 2007
    Posts: 516


    It'll make your ride go in circles..............

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