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  1. #1

    Boring Pump Nozzle

    2015 STX15f.

    Is there any rule of thumb on boring the nozzle out? With an Impeller 1 degree of pitch is roughly 100-150 rpm change. Since its easier to swap a nozzle than an impeller and my goal is to add mods incrementally. In a perfect world I would reach my end speed and rpm using all off the shelf parts, however this will never be the case.

    Has anyone bored the exit nozzle on their STX15f? Thinking of keeping a spare on hand 1-2mm larger to do some final test and tune once I've done all other mods.

    Please share your thoughts


  2. #2
    RLACEMAN's Avatar
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    I have went slightly bigger & slightly smaller & don't have any definite results yet, I did notice with my current impeller that slightly larger reduces my holeshot cavitation a little, I didn't have enough space or time to test out top speed difference, I have only had a chance to get to the big lakes once this season, the main lake I test on is small & if there is traffic its impossible to do much testing.

  3. #3
    Greg,

    I have a new bored nozzle for sale. Fits 2006 STX1500F. It is likely the same. It is +1mm. If you are interested $100 shipped.

    Not sure what rpm gain you will get. With my Seadoo every 1 mm is about 60-80 rpm but not sure if it translates.
    Last edited by Chowski; 07-16-2015 at 12:13 PM.

  4. #4
    Quote Originally Posted by Chowski View Post
    Greg,

    I have a new bored nozzle for sale. Fits 2006 STX1500F. It is likely the same. It is +1mm. If you are interested $100 shipped.

    Not sure what rpm gain you will get. With my Seadoo every 1 mm is about 60-80 rpm but not sure if it translates.
    Chowski - Shoot, I wish you had replied about a day earlier! I bought an ugly used one from eBay and will be trying my hand at boring it on my lathe. I will keep you posted on my luck in case SHTF.

    On another note - all of the parts arrived for my DIY intake setup. I will be testing it this weekend and hopefully do not need to swap to the bored nozzle with any luck. Right now I am down about 300 RPM with the 13/21 impeller on a totally stock machine.

    Pretty fantastic huh? Total cost for the intake parts ~$20

    Also managed to snap up a used 2005 15F waterbox for $30 and hull exhaust tube for $20. Hope to see at least 200 of my lost RPM's come back up top with these mods. Based on the 80-100rpm logic (if it translates) the 1mm oversized pump nozzle should be the trick.

    Click image for larger version. 

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    Last edited by CR250Greg; 07-16-2015 at 09:16 PM.

  5. #5
    Any idea how to remove the siphon tubes in the nozzle? Are they cast in or are they press fit? I wasn't able to get them to come out by any means.

    Since its just for testing purposes I might as well JB-Weld the siphon tubes and grind them flush. I wasn't able to get it on my lathe so I ended up using a fly cutter on my mill to enlarge the diameter to 83.5mm. Looks rougher than it actually is.

    Think I should be concerned about the siphon tubes being a little on the short side?


    Click image for larger version. 

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    Last edited by CR250Greg; 07-16-2015 at 09:10 PM.

  6. #6
    RLACEMAN's Avatar
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    the nozzles are not removable, you could drill them out & reinstall something similar. I just shortened them before I sent them to the machine shop. I would be curious if this will bring your rpms up a bit & what difference it makes on speed. Your DIY intake kit should bring your rpms up 1-2 bars on the tach. I would put the intake on first try it, then the nozzle.

  7. #7
    The plan for this weekend is to test the intake and see how it goes. I will still need to bore the steering nozzle as well to accommodate the pump nozzle or risk straining the steering cable.

    As it is with the 13/21 I'm turning 7150 rpm on flat and 7200 on light chop using my tiny tach as reference. If I pick up one bar that should be close to 150-200rpm and I'll be back to 7400 again.

  8. #8
    So the verdict is in on the intake - it was only good for 50 rpm up top. Right now I am looking at a steady 7200rpm. Humidity was a little on the high side yesterday, so I am figuring closer to 75-100 rpm in optimal conditions. This improvement would likely be more with a stock impeller under a lighter load. The throttle response comes on like a switch now, it is very responsive down low and in the mid range. Also cruising at lower RPM's ~4500 seems effortless, whereas with the stock intake it felt like it was lugging. I'll be making some more modifications to the intake over time, perhaps switching to a 3.5" filter setup.

    I had to get a little creative with some plumbing parts to make this work.

    Click image for larger version. 

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    The total parts list for the intake for anyone who wishes to duplicate the design.
    - 2.75" silicone Hose
    - 2.75" eBay air filter (any type)
    - 2.75" Aluminum tube w/1" T fitting
    - 3x 3" hose clamps
    - 2x 1" hose clamps
    - 3" of 1" diameter clear vinyl tubing
    - 3/4 NPT x 1/2" brass hose barb.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  9. #9
    RLACEMAN's Avatar
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    You should have gained more with that intake mod, I think you should go back to the stock impeller, the 13-21 is too much, & I bet with the stock impeller you will be between 7500-7600 rpm. Try your bored out nozzle first though, its easy enough to change out & may give you the rpms you are looking for.

  10. #10
    Quick update. Bored nozzle to 83mm straight Bore. Ran great... Still at 7350rpm and 61mph. Weather was hot however, 90 degrees with water probably 75-80 also. Really pulls your arms out between 10-40

    I am expecting 7400 when the temperature comes back down to 75.

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