Diesel engine Gear ratio

Discussion in 'Diesel Engines' started by MihaS, Feb 10, 2016.

  1. MihaS
    Joined: Jan 2011
    Posts: 45
    Likes: 2, Points: 8, Legacy Rep: 29
    Location: Adriatic

    MihaS Junior Member

    Diesel engine outdrive Gear ratio

    Hello to all,

    i have question about gear ratio for Mercruiser outdrive if im in right thread, if not change it.

    So im marinising diesel engines,turbo intercooled 3.8l,6ciy inline, 165ps(but i increase power to cca 190ps. I also attach their specifications.

    Engine have 400nm of torque at 2000rpm. You can see all power detail from chart.(metric and imperial)

    My question is what kind of gear ratio do you think that i attach for first run.


    Maybe you have similar aplication in yours craft please share.


    Boat is 25ft pleasure ,with cca 2100kg with engine and all equipment.


    Thanks


    Best regards

    Miha
     

    Attached Files:

  2. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Depending on model:

    Bravo one: 1,5:1;
    Bravo two: 2,2:1;
    Bravo Three: 2,0:1;
     
  3. MihaS
    Joined: Jan 2011
    Posts: 45
    Likes: 2, Points: 8, Legacy Rep: 29
    Location: Adriatic

    MihaS Junior Member

    Baeckmo thanks for fast reply,

    i checked for previous models of mercruiser engines (D TRONIC),they have diferent posibilities for bravo drives. But this depends on boat weight or..

    What do you think about Alpha drives, i know that you all know that they are not SO strong and... But spare parts and price for buying them is better then bravo drives.
    What could go wrong with alpha
    Also alpha is/was also connected to strong V8 gas engines up 300PS.

    Also alpha is connected with new mercruiserd diesel 4cyl engine, 2.0 with 170PS and 310nM of torque.

    Thanks
     
  4. 7228sedan
    Joined: Nov 2009
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    Location: New Jersey USA

    7228sedan Senior Member

    I wouldn't recommend an Alpha behind a diesel. I wouldn't recommend an Alpha behind a big block gas engine either. VERY light boat, maybe... I don't think the Alpha is rated for anything over 300 HP (gas not diesel). Parts availability is one thing, but reliability is the name of the game to me. I would assume that an Alpha would grenade itself behind the torque of a diesel when planing.
     
  5. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

  6. 7228sedan
    Joined: Nov 2009
    Posts: 320
    Likes: 7, Points: 18, Legacy Rep: 60
    Location: New Jersey USA

    7228sedan Senior Member

    Agreed. A new current generation Alpha... Any earlier, and I'd recommend to avoid them in a diesel.
     
  7. MihaS
    Joined: Jan 2011
    Posts: 45
    Likes: 2, Points: 8, Legacy Rep: 29
    Location: Adriatic

    MihaS Junior Member

    Hi to all,

    thanks for all answers

    Agreed about using Alpha outdrive with strong diesel engine. I will not use it:D

    But still doesnt have enough answers about gear ratio.:confused::confused::confused::confused::confused:


    Thanks

    Miha
     

  8. baeckmo
    Joined: Jun 2009
    Posts: 1,118
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    Location: Sweden

    baeckmo Hydrodynamics

    You got the answer you need already, see post no 2; what more do you expect? Everything beyond that becomes a question of propeller selection. The ratios I quoted are those giving optimum performance possibilities with avaliable propellers.
     
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