Anyone use a carb spacer on a 300 intake

Discussion in 'Other' started by gribbs, Jan 6, 2013.

  1. gribbs

    gribbs Well-Known Member

    I have seen a fella who machined some holes in his cast iron intake to accept a carb plate/adaptor and then he used an edelbrock 4 barrel carb on. Can anyone share info/pics on this from experience?
  2. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    You might get more responses in the small block section.
  3. gribbs

    gribbs Well-Known Member

    True....I just figured since there isn't much action on this forum that people always check the 'New Posts' tab when they log in and would see this. Odds are no one has anyways and I will pick up an intake and have to test fit myself. :cool:
  4. doc

    doc Well-Known Member

    back in the mid 60's i made a baseplate out of cardboard/rezin combo and it was a adapter/heat shield thing... and at the same time I opened the front holes up to the same size as the rear holes.... it worked very well, some gain in performance... was a half inch thick....and I installed a big carter afb.... could not afford a holley at the time....:Brow:
  5. gribbs

    gribbs Well-Known Member

    sounds pretty good guys...does that mean just opening holes and not needing any sort of spacer would enable me to just bolt on a square bore carb? If it is opening holes and building a spacer out of aluminum, I got a buddy that could probably cut me something, but that is just more cost and time.

    It doesn't help that I am new to mechanics and may not even be able to figure out how to take off the old carter just to clean it up myself :(

    Ponch - Can you take a few pics, maybe that would help me visual things.
  6. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    If that's a Carter AFB on your 300 its a square-bore already.
    Did you mean widen the secondaries to install a spread bore carb?

    Along Docs suggestion, I've seen guys use plywood and there's a special paint/finish you can use, that you could easily cut yourself as well :)
  7. gribbs

    gribbs Well-Known Member

    Actually I was focusing in getting the new carb mounted on the 2 brl intake, totally forgetting that the intake would also need to be honed big time. Is that what you mean by 'widening the secondaries'?
  8. doc

    doc Well-Known Member

    woah,,,,,stop..... if you have a 2 barrel carb/manifold,,,, dont even think of trying to ''adapt'' any kind of 4 barrel carb to it.... it would be a bunch of expense and trouble and not very good results,,,,,i thought you had a 4 barrel carb/manifold already and was looking to improve the performance on that....
    given a 2barrel situation, you would be better off to put a bigger 2 barrel carb on ... or change to a 4 barrel intake/carb..... you could also go to a 2 barrel TBFI system, but that would be more expensive....
    Do your homework and find a bigger 2 barrel and then open up the holes in the intake to flow more.... you may have to make a adapter to fit the bolt holes,,, i do this all the time to put holley carbs on nailhead intakes....nothing to it, I use 1/4 in. mild steel plate.... just use the base gaskets for a template get your holes lined up with the centerline of the carb and cut it out,, then drill the mounting holes in the right place...your machinist friend will know how to do this.... check out the holley 2 barrel carbs for mid to late 60's ford cars and trucks... trucks like the f-250,, f350,, f600 and so on....there were some good 2 barrels on the 292 ford Y blocks too.... all of them can be used with good results.....
    Be sure to open up the air cleaner assembly to accomodate the increased flow.....
    There is actually a 500 cfm holley 2 barrel carb available that can be made to work... and that is as much flow as some 4 barrel carbs....I would use the 250 to 350 cfm version of the holley truck carbs though for decent gas mileage....
  9. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    whoops looks like we all missed that you had a 2-bbl on there already!

    a square bore is a carb where the primaries and the secondaries are the same size. You can think of it this way, the primary circuit is what your car runs on when you are at idle or cruising, it will use less fuel for better MPG. when you mash the pedal the either a mechanical linkage or vacuum opens the secondary system (or fuel circuit) opens.

    In the pictures you can see two sets of butterfly valves. On your 2-barrel you only have one set.


    Where as a spreadbore carb the secondaries are larger than the primaries.


    example of a 2-bbl carb. 087.JPG

    Thus my comment of "widening the secondaries", assuming it was possible on the paticular 4-bbl intake manifold would enlargen the secondaries on a squarebore intake to accept the larger secondaries on a spreadbore.

    wheeeew, ok sorry if I over explained or said something you already know. :)

    DEADMANSCURVE my first word : truck

    summit lists a Jet stage#1 mod'd rochester 2G 2bbl carb , $300 . 500 cfm , no choke . they list it "for circle track use" .
    go to and search "JET-37001" , will come right up . always thought they may work well on a small V8 if no 4bbl available or pricey . and look a little sneaky . anybody used those ?
  11. 300S4EVER

    300S4EVER Well-Known Member

    Back in the day, I pulled a 2 bbl rochester off of a 455 olds(68) for my 350 pontiac(69). Not only did I have definite increase in power, I had a little bit deeper roar. Raised more than few eyebrows.:bglasses:

    DEADMANSCURVE my first word : truck

    just thinkin' - first car - 64 special wagon , 300 , 3 on the tree . added mags , hurst 3 speed comp plus ( 1970-yep they had em ) and a holley 2bbl - 500 i think , ran pretty good .
    and in reference to doc's previous statement :
    holley #4412 - 500 cfm 2bbl . man choke . 50cc pump .
    holley #7448 - 350 cfm 2bbl . man choke . 30cc pump .
    both are center hung floats and use alot of the standard holley tune and performance parts .
    sure - work up a combo adapter plate/spacer , some penum work , some port matching . work out a cold air setup . hook 'er up .
    * and as a side note - anyone have any part #'s or application info on the bigger cfm rochester 2G or 2GC 2bbl carbs ?
    * did a quick yahoo search - "rochester 2g 500" - some stuff came up - one circle track mag article covered mod's .
    Last edited: Jan 14, 2013

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