1986 4.3L OMC V6 what HP at 3000rpm?

Discussion in 'Gas Engines' started by Tom Laman, Apr 23, 2017.

  1. Tom Laman
    Joined: Apr 2017
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    Location: Los Gatos, CA 95033

    Tom Laman Tom Laman

    I have a 1986 4.3L OMC V6 engine I have adapted to inboard and need to know what HP at 3000rpm is develops does anyone know what that is. It is needed to design the prop.
    Thanks for any info.
     
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    The prop would be chosen by running the boat and achieving peak RPM's with a typical load.
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You mean select the prop ? What HP is being developed at 3000rpm would depend on what load was applied, and the throttle setting. Presumably you could work out a suitable prop size by noting the original sterndrive prop size and gear ratio, and compare that with your inboard gear ratio and consult some tables. Assuming the engine is in the same boat.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The 4.3 is rated to 4400-4800 RPM not 3000. Google "4.3 omc engine torque hp graph" and you'll get the information.
     

  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Attached is a graph from Edelbrock of a Mercruiser 200hp 4.3 litre, naturally aspirated V-6

    At 3000 rpm the engine is able to put out a max of 150 hp but Mercruisers owners information suggests propping the engine so that it turns between 4,400 to 4,800 rpm at wide open throttle. Ie the engine is producing 200 hp.

    Ie you do select a prop that will absorb what the engine can provide at max at 3,000 rpm, the engine will never attain the 4,400 rpm threshold. (except perhaps on acceleration due to cavitation on start up)

    The prop horsepower absorption and the engine effective output only reach the horsepower curve once, and that will be at WOT for whatever prop you choose. The prop horsepower requirements will be below the max horsepower curve to this point

    The main reason that you do not want to run the engine at any point on the MAX horsepower line on the graph is that this is normally an extremely poor power fuel consumption spot.

    Ie say you want to cruise and use 150 horsepower.

    If you look at the graph, this engine will produce 150 horsepower from 3000 up to 5500 rpm and there will be a spot where the fuel efficiency, (efficiency in this case defined as the amount of fuel to produce 150 hp), is optimum
    Ie the least amount of fuel used to provide 150 horsepower into the prop.

    I would check out the Boattest website to look for boats similar to yours, to see what props that they used to attain mercruisers 4400 - 4800 rpm target range and the appropriate propeller. Of course you need to find one that has the same gear ratio, as what ever you are going to use.

    Or I believe that Michigan Wheel, has a prop calculator that you can provide info and gear ratio, size of prop, rpm etc and come up with an appropriate prop
     

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