design suggestions for 12'6 jet

Discussion in 'Jet Drives' started by KiwiFabricator, Sep 13, 2009.

  1. KiwiFabricator
    Joined: Sep 2009
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    Location: auckland,nz

    KiwiFabricator New Member

    I have a 12'6" shallow vee gullwing hull glasscraft (built christchurch NZ in the 70's)
    have removed 50hp redband merc outboard and now purchased a "wetjet" single stage apparently from a 800cc 110hp jetski.
    i am looking to repower the boat with either a mazda or toyota 1600cc EFI twincam as these are cheap and plentiful in NZ and i can do all the marinisation myself -- the boat is glass in construction with 3/4" timber framing and a full 12mm ply floor glasssed in - as a boatbuilder/fabricator i have no issues fitting the motor and jet unit but just looking for some advice as far as how far to mount jet nozzle from back of boat,etc and what to watch out for -- im finding it quite hard to find info on how to retrofit a jet into a previously outboard powered boat

    any idea what sort of performance to expect and is my motor choice within reason??

    pics of boat as it is are coming

    any help would be appreciated

  2. speedboats
    Joined: Jun 2006
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    speedboats Senior Member

    The 1600cc engine probably won't rev high enough for a jet ski jet pump. I think I saw a Coggan jet on TM which would be more suitable for that engine, or alternatly if you want to stay with the pump you have then try looking at an engine out of a larger motorcycle.

    The mods to the hull are simple but important, we await the pics with interest
  3. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    What revs did the 800cc unit do thats the question can move your engine forwards on a driveshaft for balance. Car engines are not rated to be run flat out for long eriods ...maybe rated for 25 % so there is another problem

    I have done the opposite on my jetski ...taken the jet unit out and fitted an outboard

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  4. MadScience_7
    Joined: Oct 2009
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    Location: Denver, CO

    MadScience_7 New Member

    If you want a small lightweight engine that likes high RPMs, look into the Mazda rotary. A naturally aspirated 13B can make 150HP and hold it at 6K RPMs just fine as long as you have adequate cooling. If you need more power than that a turbo can bump it up to 250 pretty reliably. A complete long block is under 400lbs. They're also used a lot in homebuilt airplanes.
  5. Gerald
    Joined: Oct 2003
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    Gerald Junior Member

    I am working on a similar project using a newly designed hull. It seems to me that if the Toyota can run all day long at 3,500 rpms and we put attach a 2-1 gear box we would be in the range of a wot jetski motor?
    In addition to that, jet skis use a 140 or 155 mm dia. pump for a bunch of different motors, All the same diameter impeller but the HP ratings jump from 90 up to 255. That would indicate to me that they change the impeller degrees as HP goes up or down. Let´s say that your motor puts out 100 HP at 4,000 rpm and the jet ski motor puts out 150 at 6,000. With that in mind it might be fair to say that the jet ski puts out 100 hp at 4,000. That seems to be apples to apples. You just won´t go as fast but your jet drive sure will not know the difference.
    Here is a utube site where the guy used a VW 1.9 turbo with a jet ski drive.
  6. Gerald
    Joined: Oct 2003
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    Location: Florianopolis SC Brazil

    Gerald Junior Member

    Here is antoher site you might find interesting.
    These guys are located near me. They have attached several different car engines to thier jets. Look at clients on the top line of the site to see them or click on rjet in utube.
  7. sabahcat
    Joined: Dec 2008
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    Location: australia

    sabahcat Senior Member

  8. jbm
    Joined: Nov 2008
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    Location: montana

    jbm Junior Member

    we have run the weber mpe 750
    they will rev higher for you if you are going with a jet ski type pump
    we are using a scott 7.5 " pump and custom impeller at 7000 rpm

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