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HELP 5.7 Cobra STARVING FOR AIR-gctid556433

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    #31
    "chris" post=557129 wrote:
    I will order a FA from K&N, is there a magic number of CFM's for a SBC? Can you ever go to big and have too much air flow?
    Find an on line engine CFM calculator.

    Enter your engine data and use 4,000 rpm for the calculation.

    You will be surprised at how few CFM are required at the max RPM that we operate at!

    I would agree....... larger would be better!
    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

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      #32
      Would you not want at least what your carb is rated for? If you have a 625cfm, 650cfm. 750cfm whatever should this not be the bare minimum cfm. ??

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        #33
        "INDIGO2556" post=557173 wrote:
        Would you not want at least what your carb is rated for? If you have a 625cfm, 650cfm. 750cfm whatever should this not be the bare minimum cfm. ??
        We can run the same calculations to determine which CFM carburetor is required for a given engine.

        Keep in mind the rpm at which we operate at. Typically, we do not operate above 4000 RPM. So for example, it becomes rather pointless to run the calculation numbers for 6000 RPM.

        .
        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

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          #34
          Gonna grab a vacuum guage as was suggested, will post the reults.

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            #35
            Most recommended rpm at wot is 4200-4600 some are more.

            At that rpm short bursts in case of emergency.

            However there must be enough air flow for the wot rpm.

            A Rochester 4 barrel or 2 barrel should have more then enough air flow.

            Why are we complicating this ?

            Let's wait for the op to post back after the vacuum test.
            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

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              #36
              "Chief Alen" post=557397 wrote:
              [size]2 wrote:
              Most recommended rpm at wot is 4200-4600 some are more.

              At that rpm short bursts in case of emergency.

              However there must be enough air flow for the wot rpm.

              A Rochester 4 barrel or 2 barrel should have more then enough air flow.

              Why are we complicating this ?

              Let's wait for the op to post back after the vacuum test. [/size]
              ******************

              Chief, there is no complication here, nor any disagreement re; that the air flow (in CFM) should be more than adequate.

              We all know that our WOT RPM is used for testing only.

              Here's the result of a quick CFM calculation value for a 5.7L Marine Engine @ 4k rpm.

              [color]#0000bb wrote:
              Aprox 344 CFM Needed for a 350 CID Stock Engine [/color]


              The average Q-jet is going to easily handle this volume.

              The Q-jet's spark arrestor should also handle this volume. If it does not, replace it with a less restrictive one!

              .
              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


                #37
                Some years ago a problem like this came up when someone replaced an engine with a larger one. The solution was more air vents. The boat design was vents for the smaller engine. Enlarging the vents solved the problem.

                So it would seem the air flow on some boats is just enough with nothing extra.

                One could conclude if something was added that restricted the flow problems could arise.

                Back to the original problem.

                This might solve the problem also. http://www.amazon.com/Sierra-Interna.../dp/B0001CLFKG

                Better prices are available than here. Check Iboats for one. If there is room it is taller and would give more air flow. Search the part number.

                Doug
                Started boating 1955
                Number of boats owned 32
                Bayliners
                2655
                2755
                2850
                3870 presently owned
                Favorite boat. Toss up. 46' Chris Craft, 3870 Bayliner

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