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Mercruiser 5.7 vortec compression

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  • Mercruiser 5.7 vortec compression

    Hi guys some input would be great and possibly put my mind at ease. My 5.7 vortec motor has had a complete rebuild and after putting around 15hrs on it now to break it in I’ve just pulled the oil and checked the compressions and all 8 cylinders are 150psi my question is the vortec engine my higher compression than that?? Engine runs great apart from that.

  • #2
    150 is perfect

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    • #3
      even the mercruiser manuals used to state 150 psi for cranking compression readings
      Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

      1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

      Past Boats
      1970 Wooster Hellion - Merc 9.8
      2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
      1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

      What’s behind you doesn’t matter.Enzo Ferrari

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      • #4
        Thanks for your reply’s, I always thought the should be around 175psi

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        • #5
          only if you fill the cylinders with water or oil first
          Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

          1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

          Past Boats
          1970 Wooster Hellion - Merc 9.8
          2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
          1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

          What’s behind you doesn’t matter.Enzo Ferrari

          Comment


          • #6
            Originally posted by Andy456 View Post
            Thanks for your reply’s, I always thought the should be around 175psi
            Yup, agree with that. I've had vortec heads cracked between the inner exhaust valves 4,6 n 3,5 and those inner cylinders were 150. the outside cylinders were 175. Seen them in the 185 range as well on good running engines
            1999 Powerquest 260 legend
            502 mpi
            B1

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            • #7
              A different cam and different oil will raise that number too. Boats need conservative cams.
              87 Formula F223LS, 2016 383 Stroker, 97 Alpha Gen II Drive, 2019 Davis (HEI) Ignition, Quickfuel Marine 750 carburetor.
              Lake Winnipesaukee, NH

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              • #8
                If my valves were not adjusted correctly would this cause compressions to be low? I did them with the engine running and adjusted the valves a half turn after the rockets started clacking??

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                • #9
                  Possibly, Do a leak down to see if your guy did a good job or not
                  1999 Powerquest 260 legend
                  502 mpi
                  B1

                  Comment


                  • #10
                    If the valves are tight adjusted enough to loose compression, then you can easily find it if the motor cranking rpms increase and desincrease.

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                    • #11
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                      Originally posted by Andy456 View Post
                      If my valves were not adjusted correctly would this cause compressions to be low? I did them with the engine running and adjusted the valves a half turn after the rockets started clacking??
                      at 150 PSI you are within spec and not low.

                      so what is the problem?

                      if you have a compression reading above 150, check your gauge or you have water or oil in the cylinder.
                      Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

                      1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

                      Past Boats
                      1970 Wooster Hellion - Merc 9.8
                      2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
                      1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                      What’s behind you doesn’t matter.Enzo Ferrari

                      Comment

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