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  1. #1

    Project cheap trick

    I bought a 2016 STX15F with less than 40hrís. I would like to supercharge it.

    A little about my background. I have been involved with drag racing for the last 30yrís I have built more than 1 4 digit HP turbo cars. I know what is involved to make this happen.

    What I want from my 15F is about 200hp. Enough to pull hard and run in the upper 60ís maybe 70ísh Those are my goals.

    I want to do this using some factory Kawi parts.
    My ski is drive by cable. The supercharged Kawiís using a cable operated throttle body that I have found is the 250ís and 260ís

    First question. Will a Ultra 250 or 260 ecm plug into my 2016 15F harness? Yes or No.

    Kawi used the speed density system so Iím sure the map sensor will need to come from the 250/260 system.

    I am not using a roots blower on my ski. Rotrex is the supercharger that will be used.

    My plan is to buy factory supercharged pistons or forged replacements to lower the competition. I plan to used factory injectors to match the year of the ecm if that is a plug and play.

    I know the 15F pump bearing will not live under the extra load so I have plans to address that. I have full blown machine shop with CNC lathes and Mills. What I canít buy I can make.


  2. #2
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    I am currently in the process of building a 15f motor for boost, not to shit on your plans but almost none of what you are saying will work.

    The deck height of the 15f cylinders is different from the 250/260 and 300/310 which means you can't use any of the boosted pistons. The cylinders don't interchange.

    The harnesses and ECUs are not cross compatible.

    Kawasaki uses a mixed mode ecu that is speed density down low and alpha n up high. I would not try and run a centi supercharger on a roots/tvs map.

    The 15f pump shoe can be modified to fit a 155mm pump from a first gen ultra (250, 260, lx) and uses the same driveshaft splines. It basically drops in once you cut the shoe to fit the bigger pump seal.

    Performance parts for the 15f motor are getting really hard to find, pistons specifically. I scored a set of 9.6:1 MTC pistons and I have a used set of 10.5:1 MTC that came in the motor I am rebuilding. No one is making pistons for them anymore though unless you order custom ones.

    Hope that helps, I suspect its probably not what you wanted to hear though.

    Sean

  3. #3
    Thank you for informing me. I got the answers I was looking for. I can run a stand alone ecm. I’m guessing the deck height is taller on the Ultras? Custom pistons are something I had to deal with on most drag car motors so nothing new there. As long as the rod is short enough to give me room to make the motor 9:1.

    Sean where can I find the spec’s things like deck height, rod length and other engine spec’s?

  4. #4
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by TT350 View Post
    Thank you for informing me. I got the answers I was looking for. I can run a stand alone ecm. I’m guessing the deck height is taller on the Ultras? Custom pistons are something I had to deal with on most drag car motors so nothing new there. As long as the rod is short enough to give me room to make the motor 9:1.

    Sean where can I find the spec’s things like deck height, rod length and other engine spec’s?

    Rods are the same on everything except the 12f, deck height I couldn't tell you. There is a thread in the tech tips and info section that has some of it.

    On the old riva boats, they used to run 10.5:1 with a 1mm base spacer. I didn't want to use the spacer so I chucked it in favor of a deeper dished piston.

    The 15f pistons are kind of sketchy where boost is concerned. They are really more of a high compression na design (they are zx12r based). The ring lands are real thin and the wrist pin sits closer to the top.

    Sean

  5. #5
    I was thinking a spacer would provide some room for more piston pin height for a deeper dish and thicker ring lands. Provided the piston dose not get pulled out of the cylinder to far at BDC. I may look at what the motorcycle guys are doing and see how
    similar the engine architecture is to the watercraft motor. A 30% power increase would put me at my goal. That’s about 5lbs of boost. The motor in stock form should handle that with 92 octane pump gas and a good tuneup.

  6. #6
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    You run into cam timing issues and timing chain length issues with base spacers.

    200hp is doable with higher comp pistons and bigger cams in na form.

    Sean

  7. #7
    I have been talking to some bike racers that get 180hp out of there 1200's But that is throttle body per cylinder 11,000+ rpm and the motor is a turd up to 6500-7000.
    If I could get 200hp with a proven combo, Cam's pistons and a tune I would go that route. I have a good friend that is one of the best hand porters in the country. I bet there is money on the table with a port job.

  8. #8
    Let me out of here......I need to go on Greenhulk!
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    Wouldnt you be better off buying a hull for $500 and a used motor for $1500. Everything else will pretty much be not stock

  9. #9
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    Quote Originally Posted by smokeysevin View Post
    You run into cam timing issues and timing chain length issues with base spacers.

    200hp is doable with higher comp pistons and bigger cams in na form.

    Sean
    Thats what i was thinking as well. NA with higher comp pistons and a few bolt ons should get you to 200hp. There are plenty of casting marks in teh intake and exhaust that could be smoothed out and pump work will net some gains as well. Otherwise i might be inclined to install a 4tec motor like that project your working on Sean.

  10. #10
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Je 9.8:1 zx12r pistons are pump gas safe and right around 12:1in the 15f motor, that plus zx12r cams and some porting will put you right around 200hp. I ran that setup and it ran 70 with a shitty tune on the 155mm pump. With a proper tune it would have been 72-3. The stx hull takes 250hp to go 75ish.

    Sean

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