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Outdrive Gear Ratios

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  • Outdrive Gear Ratios

    Can someone go into detail about pro's/cons of installing a 1.32 outdrive on my small block. Boat is a 22' formula with a 5.7L engine. Ive seen a million postings about going from 1.32 to 1.47 on big blocks and the dangers posed, but I cannot find any advice on going the opposite direction. Any help would be appreciated!!

  • #2
    Originally posted by gregfeld1 View Post
    Can someone go into detail about pro's/cons of installing a 1.32 outdrive on my small block. Boat is a 22' formula with a 5.7L engine. Ive seen a million postings about going from 1.32 to 1.47 on big blocks and the dangers posed, but I cannot find any advice on going the opposite direction. Any help would be appreciated!!
    I can give the reason I am going from a 1.32 to 1.50... which may provide SOME insight. But, I'll leave it to those with more experience to provide the specific details.

    With the 1.32 (which is for a bigger block engine?) the engine works to get up to speed. It's almost like trying to accelerate a car from a dead stop by using 2nd gear. You can do it, but engine works hard until it gets up to a certain speed. It will get up to speed but the engine works to do it. So, I have to believe it is not the best thing for the engine. Plus, it makes the boat more difficult to maneuver at slow speeds, like when docking.

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    • #3
      Originally posted by gregfeld1 View Post
      Can someone go into detail about pro's/cons of installing a 1.32 outdrive on my small block. Boat is a 22' formula with a 5.7L engine. Ive seen a million postings about going from 1.32 to 1.47 on big blocks and the dangers posed, but I cannot find any advice on going the opposite direction. Any help would be appreciated!!
      Your hyjacking a thread, please start your own thread
      94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
      95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
      07 Seadoo GTX
      Merc Adults Only VP Adults Only
      G-Dad always said "First Liar doesn't stand a chance"

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      • #4
        Originally posted by AllDodge View Post

        Your hyjacking a thread, please start your own thread
        Ayuh,..... This might work better,.......

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        • #5
          Originally posted by gregfeld1 View Post
          Can someone go into detail about pro's/cons of installing a 1.32 outdrive on my small block. Boat is a 22' formula with a 5.7L engine. Ive seen a million postings about going from 1.32 to 1.47 on big blocks and the dangers posed, but I cannot find any advice on going the opposite direction. Any help would be appreciated!!
          the same reason you dont pedal a bike starting out in 10th gear. or try to drive a VW bug in stop-n-go traffic while in 4th gear

          you would over-load the small block, causing it to lug...leading to detonation and a hole in each piston.

          the 1.32:1 ratio needs the torque of a big-block to spin the prop enough.

          the problem is the alpha's then grenaded due to the torque.
          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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          • #6
            Sign up today
            Howdy,

            Welcome aboard!

            First of all, it might be helpful for you to have a look at the following thread for future questions.....
            https://forums.iboats.com/forum/engi...-faq-for-i-o-s

            Also, take a look at:
            https://forums.iboats.com/forum/foru...ules-attention

            ---------------------------------------

            There are additional reasons why a higher ratio drive is not used on a small block (read lower torque engine... )

            While you *could* probably get it to work by using a lower pitch prop, it would be less efficient.

            For most all recreational planing type watercraft, manufacturers have recommended (in general) to always select a prop-pitch that will provide maximum speed (optimum, weight, CG, at sea-level, trim etc) at maximum rated engine RPM. (those same manufacturers already provided the "right" drive ratio)

            Propeller manufacturers design props to operate with a rather specific RPM range. (racing props and surface drives, etc excepted)

            I.E, there is an RPM upper-limit where any prop will become inefficient......such that above that upper limit, the hydrodynamic drag becomes so great that turning it any faster doesn't give you much more thrust. (this is true for any prop turning in either liquid or air)

            Same thing applies with pitch. There's a maximum pitch that either results in an aerodynamic stall in air, or cavitation in water. In air, there's also max RPM that produces prop-tip velocities that can exceed the speed of sound.

            In all cases thrust is lost.

            The point of all this is that to keep the propeller RPM in the range that is most efficient for the pitch you have and use gears to operate the engine in it's most efficient range.

            If you get out of either the optimum range for the engine or the prop, you will lose efficiency.

            Get out of the range for both, you lose even more......

            The engine, drive and prop designers already "did the math"

            Cheers,

            Rick





            1987 FourWinns 211 Liberator, Re-powered in 2006 with a 1997 Mercruiser 7.4L Bravo III
            Originally an OMG 460 King Kobrah!!
            .
            2003 Zodiac Zoom + Tohatsu 9.8 4-stroke

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