SB engine vacuum ports - NCRS Discussion Boards

SB engine vacuum ports

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  • Jon W.
    Expired
    • August 31, 1996
    • 15

    SB engine vacuum ports

    Subject is a '70 Corvette - Upon swapping the Holley 600cfm vac. secondary for a 750 cfm mech. atop a Edelbrock Performer RPM, the vacuum fitting (from the original L-46 manifold)that supplied the PB and vacuum-powered doors, etc. no longer cleared the new carb. (Secondary fuel bowl extends farther rearward). I'm already using a 1/4" insulated gasket. I've plugged that manifold souce and taken vac. for the PB and vacuum motors off the large nipple at the rear of the carb base (below throttle blades). I've also routed the PCV valve to a small nipple at the right front corner of carb base(again below the throttle blade), but am not sure if this will provide enough flow for PCV system and if this source will cause some unbalance in the idle mixture on the primary side.

    Now the question(s) is/are: 1.) would I be better off using the single larger vac. fitting at the base of the secondaries for all three (PB, vacuum motors, AND PCV) or 2.) shall I try to locate or make a low-profile manifold fitting and use it for PB and vac. motors (as original) and use the large carb base fitting (at rear) for PCV only or 3.)I'm OK as configured? Thanks.
  • Tom H.
    Expired
    • May 31, 2003
    • 89

    #2
    Re: SB engine vacuum ports

    A place called Mo'Speed is making a fitting just for the combination that you have. It is designed to fit under the holley and supply normal vacuum.

    Mo' Speed

    1238 N Bryan

    Nixa, Mo. 65714

    Phone: 417-724-2118
    You might try them if your currant set-up isn't working.

    Comment

    • Joe L.
      Beyond Control Poster
      • February 1, 1988
      • 43221

      #3
      Re: SB engine vacuum ports

      Jon-----

      Your best source of vacuum is the manifold fitting. If the source that Tom suggested can provide a low profile fitting, that's going to be your absolute best solution. Otherwise, you can easily make a low profile adapter for the fitting using pipe and/or tubing fittings available at a hardware store. It won't look "correct", but your whole carb set-up is not correct so a little more "uncorrectness" is not going to be that big of a deal. However, a low profile fitting from the source that Tom suggested will give you the cleanest installation and that's what I'd go for.
      In Appreciation of John Hinckley

      Comment

      • Patrick H.
        Beyond Control Poster
        • December 1, 1989
        • 11643

        #4
        Re: SB engine vacuum ports

        "your whole carb set-up is not correct so a little more 'uncorrectness' is not going to be that big of a deal."

        But of course, the cleaner and more correct appearing the installation, the less it will look like Bubba got a hold of the car. And we all know that Bubba has seen WAY too many Corvettes.

        Patrick
        Vice-Chairman (West), Michigan Chapter NCRS
        71 "deer modified" coupe
        72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
        2008 coupe
        Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

        Comment

        • John H.
          Beyond Control Poster
          • December 1, 1997
          • 16513

          #5
          Re: SB engine vacuum ports

          Edelbrock makes a low-profile brass vacuum fitting specifically for your application, to fit under a Holley rear float bowl - any speed shop has them.

          Comment

          • Jon W.
            Expired
            • August 31, 1996
            • 15

            #6
            Re: SB engine vacuum ports

            Tom, This appears to just what I am looking for. I called MoSpeed, had a nice conversation with Randy (very helpful) and ordered the piece. It is reported to be even lower profile than the Edelbrock part and has capability to connect 3 vacuum lines if needed. Part can be seen via attached link. Thanks to all for your help.




            Low profile vacuum fitting

            Comment

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