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will a squarebore to spreadbore adapter plate effect performance?

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  • will a squarebore to spreadbore adapter plate effect performance?

    The manifold i got for my vortec engine is a dualplane squarebore carb setup. I want to use my quadrajet for the time being and that's a spreadbore. I have a 1 inch thick adapter plate that will allow me to mount the quadrajet. Will this cause any performance issues?
    1986 searay 268 weekender "lunasea" (current)
    1986 grady white 24 offshore with twin 150 yamaha's(current)
    1979 grady white 201 marlin (sold)
    1991 seapro centra 190
    http://picasaweb.google.com/lime4x4/Lunasea#
    https://picasaweb.google.com/lime4x4...hite201Marlin#


  • #2
    Re: will a squarebore to spreadbore adapter plate effect performance?

    90% of older chev small block and V6 manifolds are already poo by design.

    Here's a simple way to check if it's going to effect performance:

    Does the manifold/adapter plate combination have a smaller opening than the 4 barrels on the carb?

    So long as you're not introducing a restriction, it should be okay.

    In fact, in a lot of cases, introducing a spacer can actually help performance.

    Comment



    • #3
      Re: will a squarebore to spreadbore adapter plate effect performance?

      Originally posted by lime4x4 View Post
      The manifold i got for my vortec engine is a dualplane squarebore carb setup. I want to use my quadrajet for the time being and that's a spreadbore. I have a 1 inch thick adapter plate that will allow me to mount the quadrajet. Will this cause any performance issues?
      as long as it's not an open spacer you'll be fine, will probably have to adjust idle a/f mixture slightly

      Comment



      • #4
        Re: will a squarebore to spreadbore adapter plate effect performance?

        this is the one i have
        http://www.mr-gasket.com/ProductDeta...minselection=0
        1986 searay 268 weekender "lunasea" (current)
        1986 grady white 24 offshore with twin 150 yamaha's(current)
        1979 grady white 201 marlin (sold)
        1991 seapro centra 190
        http://picasaweb.google.com/lime4x4/Lunasea#
        https://picasaweb.google.com/lime4x4...hite201Marlin#

        Comment



        • #5
          Re: will a squarebore to spreadbore adapter plate effect performance?

          Originally posted by lime4x4 View Post
          dont use that one, the engine will idle like **** and run like **** anything under 3/4 throttle, get a 4-hole spacer and the proper gaskets.

          Comment



          • #6
            Re: will a squarebore to spreadbore adapter plate effect performance?

            Originally posted by Rat Capri View Post
            dont use that one, the engine will idle like **** and run like **** anything under 3/4 throttle, get a 4-hole spacer and the proper gaskets.
            I don't see anything wrong with that spacer? Why do you think they even make it, if it's gonna be a problem? Plus, usually an increase in plenum height is advantageous, because it gives a longer runner to the manifold, usually increasing torque.

            Comment



            • #7
              Re: will a squarebore to spreadbore adapter plate effect performance?

              don't know about that one but i used a 4 holer and then took a die grinder to the intake so the holes funnel smoothly.
              don't remember what brand as it's been some time now.
              different engine and manifold, 390 amc and offy 360 dual port.
              crane cam and lifters plus doug thorley headers
              built to be a mid range engine and runs i think great.
              1968 amx with only 53k miles on the o.d.
              sets in my sons garage now and is his.
              when he was in iraq he asked me how the amx was doing.
              i asked him if he wanted it, quick reply h*** yes!
              then i told him all you have to do is come home alive and it's yours.
              i think i got a bargan.
              opps, sorry but that's how i matched a spread bore double pumper.

              Comment



              • #8
                Re: will a squarebore to spreadbore adapter plate effect performance?

                Cool car, Mark Donahue come to mind. that spreadbore adapter will just fine you probably wouldn't feel the difference.
                '90 Chaparral 2000SL
                5.8 Cobra
                '67 MFG Westfield Regal
                80hp V-4
                (No private messages)

                Comment



                • #9
                  Re: will a squarebore to spreadbore adapter plate effect performance?

                  The manifold i got for my vortec engine is a dualplane squarebore carb setup.
                  Ayuh,... I agree,... Why would you want to put an Open plenum over a Dual Plane manifold,..??
                  Any Grease is Better,..... Than No Grease at All.......

                  Comment



                  • #10
                    Re: will a squarebore to spreadbore adapter plate effect performance?

                    it's not going to stay that way.. In a month or so i want to replace the quadrajet with an Edelbrock 1409 in a month or so
                    1986 searay 268 weekender "lunasea" (current)
                    1986 grady white 24 offshore with twin 150 yamaha's(current)
                    1979 grady white 201 marlin (sold)
                    1991 seapro centra 190
                    http://picasaweb.google.com/lime4x4/Lunasea#
                    https://picasaweb.google.com/lime4x4...hite201Marlin#

                    Comment



                    • #11
                      Re: will a squarebore to spreadbore adapter plate effect performance?

                      Originally posted by MikDee View Post
                      I don't see anything wrong with that spacer? Why do you think they even make it, if it's gonna be a problem?
                      it's not a problem if yhe engine stays above 4500 rpms all the time

                      Originally posted by MikDee View Post
                      Plus, usually an increase in plenum height is advantageous, because it gives a longer runner to the manifold, usually increasing torque.
                      that's only true if velocity increases or at least stays the same, that's not gonna happen with that open hole spacer......should only use a spacer for the manifold type you're using

                      Comment



                      • #12
                        Re: will a squarebore to spreadbore adapter plate effect performance?

                        so i should get this type of spacer then??
                        http://cgi.ebay.com/ebaymotors/EDELB...Q5fAccessories
                        1986 searay 268 weekender "lunasea" (current)
                        1986 grady white 24 offshore with twin 150 yamaha's(current)
                        1979 grady white 201 marlin (sold)
                        1991 seapro centra 190
                        http://picasaweb.google.com/lime4x4/Lunasea#
                        https://picasaweb.google.com/lime4x4...hite201Marlin#

                        Comment



                        • #13
                          Re: will a squarebore to spreadbore adapter plate effect performance?

                          Personally, I don't think it matters one way or the other

                          Comment



                          • #14
                            Re: will a squarebore to spreadbore adapter plate effect performance?

                            From Dennis Moore:

                            CARBURETOR TO MANIFOLD ADAPTERS
                            When General Motors' Rochester Division decided to quit making the
                            Quadrajet carburetor, Mercruiser switched to the Weber carburetor.
                            Unfortunately the Quadrajet four barrel is a spread bore design
                            carburetor and the Weber is a square bore. All Chevrolet marine engines
                            with standard performance intake manifolds have the Quadrajet spread
                            bore carburetor mounting flange. An adapter is used by Mercruiser to
                            mount the square bore Weber carburetor on the spread bore manifold. This is not an ideal situation, to say the least, for maximum performance. The Rochester Quadrajet is one of the finest carburetors ever built It has
                            been discontinued because the entire automotive industry has converted to
                            fuel injection. Purchasing a used Quadrajet marine carburetor from a
                            Boat dealer and installing it in place of the Weber,and doing away with the
                            adapter,would be an excellent idea. The Weber four-barrel is also an
                            excellent carburetor. Installing a square bore intake manifold while
                            retaining the original Weber carburetor would be another good
                            option in order to do away with the adapter. Either way,getting rid of the
                            adapter should be one of your first steps for increased engine
                            performance.
                            From Mercruiser:
                            Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

                            Comment



                            • #15
                              Re: will a squarebore to spreadbore adapter plate effect performance?

                              Originally posted by lime4x4 View Post
                              so i should get this type of spacer then??
                              http://cgi.ebay.com/ebaymotors/EDELB...Q5fAccessories
                              Ayuh,.... Actually,.. This would be the Best adapter to use,...


                              You're gonna change it in a month or so,...
                              Break out the plastic,+ do it Right the 1st time,.....
                              Any Grease is Better,..... Than No Grease at All.......

                              Comment

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