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  1. #1
    mjh3ides's Avatar
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    Need impeller pitch advice

    I've been experimenting with different props on my GPR and could use some advice what to try next. First I tried a 15/23.5 DF and got 7300 rpm, then lost .9mph @ 7200 with a 15/25 setback DF. I'm considering repitching the 15/23.5 to 14/25. What do you guys think?


  2. #2
    alex29573's Avatar
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    what size nozzle are you using?

  3. #3
    mjh3ides's Avatar
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    85mm

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    Moderator OsideBill's Avatar
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    It all depends on RPM's and how much you are stuffing the pump. What grate are you running? The 800 grate will stuff the pump less and give you better rpms, resulting in higher speeds. The 1200 grate will cause an overstuff situation, that you will need to relieve. The rule of thumb is to pitch up until you lose rpm's. Different style impellers yield varying results too.

    http://www.greenhulk.net/forums/showthread.php?t=41528

  5. #5

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    Cool

    Quote Originally Posted by mjh3ides View Post
    I've been experimenting with different props on my GPR and could use some advice what to try next. First I tried a 15/23.5 DF and got 7300 rpm, then lost .9mph @ 7200 with a 15/25 setback DF. I'm considering repitching the 15/23.5 to 14/25. What do you guys think?
    I agree with Mr Bill BUT who bent the props? It seem different people's method of tweeking props offer different # with your set up(seem 1390) best bet shifting over to one of the vx/4-stroke boat props- but thats just me

    later CD

  6. #6
    mjh3ides's Avatar
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    I'm using the 1200 for now. My goal is to achieve 79-80 with a decent holeshot before switching to the 800 grate & VX impeller. Both were done by Impros but the 15/25 is setback. I know every boat has a different sweetspot in the rpm range, but after looking at many other people's setups it seems that most stay with a 14 leading edge pitch. I'm just not sure how a 15/25 will compare to a 14/25.

  7. #7
    philip_gpr's Avatar
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    14 will spin up a little easier from idle

    I bet in the mid and top you won't be able to tell the difference between a 14 or 15

    if the 15/23.5 DF is faster don't touch it - it sounds like it is working great right now - so work on the other one and try to get it faster than the 15/23.5 DF

  8. #8
    3 x 1800 feeding my obsession sconti stellari's Avatar
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    a bigger exit nozzle would yield more rpms but not sure if it will work with 1200 grate

  9. #9
    mjh3ides's Avatar
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    Quote Originally Posted by philip_gpr View Post
    14 will spin up a little easier from idle

    I bet in the mid and top you won't be able to tell the difference between a 14 or 15

    if the 15/23.5 DF is faster don't touch it - it sounds like it is working great right now - so work on the other one and try to get it faster than the 15/23.5 DF
    I'm starting to think about putting aside the setback prop until I get closer to being tuned in and pick up a second non-setback DF so I'm comparing apples to apples. Am I correct that a setback prop will give a better holeshot at the expense of rpm's on top? The 15/23.5 was faster @ 7300 but I still have the high speed pot @ 11. Won't I be out of the powerband pretty quickly when I start to run it a bit leaner? I turned it 7380 with the extra oil in the break-in fuel.

  10. #10
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Quote Originally Posted by mjh3ides View Post
    I'm starting to think about putting aside the setback prop until I get closer to being tuned in and pick up a second non-setback DF so I'm comparing apples to apples. Am I correct that a setback prop will give a better holeshot at the expense of rpm's on top? The 15/23.5 was faster @ 7300 but I still have the high speed pot @ 11. Won't I be out of the powerband pretty quickly when I start to run it a bit leaner? I turned it 7380 with the extra oil in the break-in fuel.
    For the 1390 efi if your going to run a dynafly the best pitch is a 14/25 setback with a 85 mm nozzle. Like the one I'm selling in the yamaha classifieds on my ski that impeller with a 1200 grate ran 80.6 MPH. It will have a wicked hole shot and i was turning about 7230 rpm's
    selling it because i went with a VX. If you have any questions about your set up feel free to call me at 727-365-5132 Thank you, Jim

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