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Lightened boat, same speed?

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  • Lightened boat, same speed?

    So glad to be a new member of this forum. My recently purchased 1977 Aquasport 222 has a "marineized" 350 sbc and I was told is a 300 hp. Good luck! With a dual-control full tower it would run 18 mph @ 3,800 rpms. To gain more speed I removed the tower to get the weight down. Now it runs the same18 mph at 3,800 rpms.
    Maybe a prop or a tranny issue? I love the boat and can't afford a re-power. Idles smooth and timing is spot on, has new points, plugs, wires, Holley, DUI distributor, etc. Thanks for your input. Larry

  • #2
    welcome aboard

    you have a motor or prop issue

    the motor should be at 5000 RPM at full throttle


    what prop do you have?
    what gear ratio drive do you have?

    you should have a 1.5:1 drive or about there, and about a 19 or 21 pitch prop.

    when was the last time you did a compression test?
    when was the last time you did a tune up?
    When was the last time you check fuel pressure from your pump?
    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


    • #3
      Being that vintage, it could be water logged also. Find the specs for the boat, and trailer and weigh it.
      If ya can't fix it with a hammer,ya got yourself an electrical problem.

      Comment


      • #4
        Thanks. Boat is restored and dry. Compression is 175 across the board, tuned up with all new tune up stuff including electric fuel pump; 4-7 psi. Engine is >< 4800 at full power. Timing is 10-degrees BTDC @ 600 rpms/ 35-degrees @ 4000 rpms. You can see why I'm stumped.

        Comment


        • #5
          I will check the prop specs (have a great prop shop close by) and the gear ratio.

          Comment


          • #6
            if your compression is 175, check your gauge. your only going to see about 150-160 psi max on a marine SBC and that is at 9.5:1 compression.
            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


            • #7
              You say the carb is a Holley. 2 bbl or 4bbl, which model? Does the throttle linkage/cable permit WOT? If a 4bbl are the secondaries free to open? Any restriction in the exhaust? Since it was a Marinized engine... any idea if the conversion included putting a marine cam? What intake manifold is on it, GM or aftermarket?

              Comment


              • #8
                Originally posted by LAWRENCE Owen View Post
                Thanks. Boat is restored and dry. Compression is 175 across the board, tuned up with all new tune up stuff including electric fuel pump; 4-7 psi. Engine is >< 4800 at full power. Timing is 10-degrees BTDC @ 600 rpms/ 35-degrees @ 4000 rpms. You can see why I'm stumped.
                so the motor does go to 4800 RPM at WOT under load? what is your speed at WOT? GPS speed, not the crappy speedometer speed

                if so, what is the problem? you give a 18mph at 3800 RPM. it was assumed that is all it had. if you truly hit 4800 at WOT, that is simply an arbitrary point in the middle of the prop curve. if that is the case, hull shape, prop pitch RPM of engine, prop slip and gear ratio all come into play, however weight doesn't.

                please clarify. most likely you removed everything for nothing.
                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


                • #9
                  I'll get the numbers and the info you suggest, and see what the speed is at 4800. Should have done this. Carb is new Holley 650 marine 4bbl atop what looks to be the stock GM intake and the linkage is correct. Secondaries are opening; too easily in my estimation -- when I accelerate beyond the 3800 cruising rpms. Exhaust is straight thru, raw salt water cooled.

                  Comment


                  • #10
                    Cruise is generally about 3000-3400 RPM, however usually determined with a fuel flow meter.

                    above 3800 RPM is normal for the secondaries to open on an SBC, your loading your motor and demanding more power you can change the springs in the vac chamber if needed. what are the holley carb numbers, this will determine what the setup should have been.
                    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


                    • #11
                      Holley 650 Spreadbore 0-80552. It's the 4bbl I have. A 350 turning 5000 rpm is not going to use all of that carb, the secondaires when open 50 percent, will be more than enough. It is jetted a bit rich on the secondary side
                      Click image for larger version  Name:	large0-80552.jpg Views:	1 Size:	155.9 KB ID:	10691478

                      Comment


                      • #12
                        Yes, jimmbo, this Holley 0-80552 is the carb. I will get the prop specs asap. My logic is if the current prop is pushing the boat only 18 mph, a larger, pitch-correct prop will push the boat faster at 3800 rpms. Is my thinking correct?

                        Comment


                        • #13
                          no, going to a bigger prop will most likely lug the motor and kill it. you prop for WOT

                          your 80552 holley is a 4175, 650 CFM, #61 primary jets, #50 power vavle and a 0.04 squirter.

                          the squirter is a bit large for the 5.7 (most are in the 0.028-0.031 range) and as Jim stated, it will run a bit rich on the secondaries.

                          you still have not posted what your WOT RPM and speed is (with a qualified tach and a GPS speed)
                          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


                          • #14
                            I'll get the boat in the water soon and supply more info. A thank you to all.

                            Comment


                            • #15
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                              Business Owner & Certifed Technician
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