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    vacuum gauge-gctid358510

    so you guys. i need to install a vacuum gauge on my 385 chevy ..i have a performer manifold with a marine quadrajet no spot for vacuum conection where do i drill? thanks ,jerry

    #2
    intake manifold..

    Comment


      #3
      Just forward of the carb " should " be a threaded plug in the intake.

      Here is a site that might help.

      http://www.secondchancegarage.com/public/186.cfm
      Be good, be happy, for tomorrow is promised to no man !

      1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

      '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

      Manalapan N.J

      Comment


        #4
        385 eh? Looks like you built yourself a .040" over stroker.

        I presume that you will reading manifold pressure for setting low speed fuel metering circuits.

        The Performer intake manifolds do offer a port, however, the port is normally located in the #8 cylinder runner.

        Not the ideal location for what you will be doing, but it should work.

        Edelbrock 2601 Performer Air-Gap intake manifold



        Edelbrock SBC Vortec Performer EPS Intake Manifold



        Edelbrock 7101, Performer RPM Dual Plane Intake



        .
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #5
          Yep, I use the port on #8 runner on my 7101. I installed a nipple / barb fitting and then put a cap on it after use.

          I may remove it as I don't think I will need it again.

          Comment


            #6
            thanks guys, goin to use the vacuum gauge to see where the sweet spot is with a more agressive prop ...can u say torque,,yep 40 over next is water injection..:

            Comment


              #7
              Brad, consider the throttle plate position per engine load per RPM and what this means in terms of manifold pressure.

              I think that you'll find it to be not very useful, and that you'd do much better with a fuel flow meter.

              Car/truck.... I'd agree with you.
              Rick E. Gresham, Oregon
              2850 Bounty Sedan Flybridge model
              Twin 280 HP 5.7's w/ Closed Cooling
              Volvo Penta DuoProp Drives
              Kohler 4 CZ Gen Set

              Comment


                #8
                2850Bounty wrote:
                Brad, consider the throttle plate position per engine load per RPM and what this means in terms of manifold pressure.

                I think that you'll find it to be not very useful, and that you'd do much better with a fuel flow meter.

                Car/truck.... I'd agree with you.
                +1

                Miles per gallon is the measure of efficiency, not vacuum.

                The vacuum is a method of setting carburator low speed jets.

                Mercruiser used to put vacuum gauges in their metering panels. They stated to "keep the needle in the green area for best performance. However, there were boat manufacturers who were putting underpowered engines in their boats (Bayliner included) and the boats would not stay on plane "in the green" so they discontinued the pactice to eliminte the complaints from the consumers. My 1968 Aristocraft had the vac gauge, but it rode way into the green at cruise speed.
                Captharv 2001 2452
                "When the draft of your boat exceeds the depth of water, you are aground"

                Comment


                  #9
                  I think what Harv and I are both suggesting, is that in order for a vacuum reading to be meaningful, engine RPM would need to catch up with throttle plate position (spelled reduced load) in order to pull enough negative manifold pressure that would offer any valuable data....... such as it can in a car/truck scenario.

                  That simply does not occur under Marine loads.

                  IOW, the open throttle plate position (required for the load) prevents manifold pressure that would tell you much of anything.

                  .
                  Rick E. Gresham, Oregon
                  2850 Bounty Sedan Flybridge model
                  Twin 280 HP 5.7's w/ Closed Cooling
                  Volvo Penta DuoProp Drives
                  Kohler 4 CZ Gen Set

                  Comment


                    #10
                    My experience with my 350 Mercruiser 21' Glastron is just the opposite. I use the vaccuum guage all the time for maximizing efficiency, and making sure I'm not working the engine too hard. You can very easily see that a gain of 5 knots for a cost of 2 on the vaccuum guage may be worth it, but a gain in .5 knots for a cost of 2 on the guage doesn't make good sense. Generally your fuel will follow your vaccuum if your carb/injection is set up right.

                    It is the best indication of load you can get. I can cruise in a range between 10 and 6.5, after that the secondaries on the quad start to open. You can actually see it on the guage.

                    If your boat is underpowered like my 2850, you're pretty much flat out all the time anyway...still good info to have and I plan to add them this spring. For $20 a pop how can you go wrong!

                    Chay

                    Comment


                      #11
                      Does anyone use a Vac gauge to set the timing? I am suspious about the timing marks on a 90 model Merc., 5.7L(fresh rebuild) engine I am working on. The vac is a little low on this one at 650 rpms. (12-13), plus I cant the venturi's to quit bribbling no matter I do or rebuild the carb a couple of times.

                      Sorry if I hi jacked the thread, but they are soooo related.

                      Comment


                        #12
                        For Marine w/out diaphram vacuum advance...... Short answer... NO.

                        However, a change to BASE advance (while idling) will cause a change to manifold pressure (aka vacuum) as you advance/retard.

                        But this is more of a result of RPM change, than spark lead.
                        Rick E. Gresham, Oregon
                        2850 Bounty Sedan Flybridge model
                        Twin 280 HP 5.7's w/ Closed Cooling
                        Volvo Penta DuoProp Drives
                        Kohler 4 CZ Gen Set

                        Comment


                          #13
                          when u here the sweet spot with a small block chevy ,the vacuum gauge will be topped out kind of handy....

                          Comment


                            #14
                            2850Bounty wrote:
                            I think what Harv and I are both suggesting, is that in order for a vacuum reading to be meaningful, engine RPM would need to catch up with throttle plate position (spelled reduced load) in order to pull enough negative manifold pressure that would offer any valuable data....... such as it can in a car/truck scenario.

                            That simply does not occur under Marine loads.

                            IOW, the open throttle plate position (required for the load) prevents manifold pressure that would tell you much of anything.

                            .
                            Rick,

                            Can you re-phrase that? I haven't got a clue about what you are trying to say.

                            Comment


                              #15
                              every engine has a sweet spot,,,

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