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  1. #1
    Hydrotoys's Avatar
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    GPRXP Open Loop Cooling

    This has been posted in a few places, but I thought since it's paramount to putting the rxp engine in the gpr, this would be a good place as any.

    This should be a good starting place using the rapid acceleration block off plate. It also uses reverse cooling, getting water to the head first. Testing has been done with this, with quite a few boats now.

    We kep the engine pressure down around 15psi-20psi using an automotive oil pressure gauge duct taped to the dash. I've since installed a small water pressure gauge right on top of the adaptor, just for a quick reference. We are using a 1/4-turn SST valve on the incoming water to the engine. We are using a 3/8" hose as a restrictor to the intercooler/exhaust side.

    Goal for temp is 150-160F to the engine.

    SandiegoJoe also has dedicated a seperate line to his intercooler and his exhaust.

    Last edited by Hydrotoys; 11-05-2007 at 12:15 AM.


  2. #2
    Hydrotoys's Avatar
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    Transom plate modification. On the above diagram it talks about opening it up to match the 5/8" water line.

    Since I was doing a new plate, I snapped a few pics, along with some sizes.

    You can also increase your water supply by using an external 2nd cooling line, and feed the intercooler directly.

    This mod is most useful for an intercooler such as the XSCOOLER that can utilize the high water flow. About all this would do for the Riva is blow the tanks off the p.o.s. so you really don't need it if using that style.

    3/8"NPT Tap.
    37/64 drill bit.
    teflon tape
    5/8"barb x 3/8"npt brass fitting.
    1/2" drill bit.

    -Remove the transom plate from the hull.
    -Remove the external press-in fitting. Best way is to tap it out by putting something in the other side.
    -Drill out the hole completely with the 1/2" drill bit all the way thru.
    -Drill out the hole, except for the last 1/8" with the 37/64" drill bit from the engine side of the plate...leave the extra material on the pump side.
    -Tap out the hole on the engine side.
    -clean with soapy water.
    -teflon tape your brass fitting and install.
    -You may have to hog out the transom hole to allow the brass fitting to fit thru.




  3. #3

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    Forgive my stupidity but I'm new to PWC's in general, so the water we use for colling the engine, is pulled from outlets in the transom plate? That I assume just pull pressurized water out of the pump tunnel, pre-impeller??? OR After the impeller, and route it back to the transom plate? Does anyone by chance have a diagram of how/where the transom plate gets its water feed? Thanks.

  4. #4
    ISLAND RACING seadoo951's Avatar
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    The water gets pulled from the pump after the impeller and goes back to the transom plate and to the motor. This is done inside the pump and is not seen from outside the pump itself. When you remove your pump, and look inside with the impeller removed, you will be able to see how the water is routed.
    Quote Originally Posted by boostaholic View Post
    Forgive my stupidity but I'm new to PWC's in general, so the water we use for colling the engine, is pulled from outlets in the transom plate? That I assume just pull pressurized water out of the pump tunnel, pre-impeller??? OR After the impeller, and route it back to the transom plate? Does anyone by chance have a diagram of how/where the transom plate gets its water feed? Thanks.

  5. #5
    cheatin' piston popper addicted's Avatar
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    Mark,

    I saw in Joe's build that after opening up this line, the ball valves that you guys use are almost closed. He proposed not drilling out the fitting, but there was never a conclusion. Not sure if I read it here or on your site. For a STOCK motor, do you think this is still necessary?

  6. #6
    Moderator Insanediego Joe's Avatar
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    Mike, I have no data to back that up. The system as described here works and works flawless...

  7. #7
    Hydrotoys's Avatar
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    Path of least resistance....

    I say it depends on what your hardware configuration is. If you are using a Riva style IC or some other highly restrictive IC, your water needs are much, much lower, than those of us using XSCOOLER style IC's. You probably don't need to drill out anything in this case, and will need the quarter turn valve just to keep the engine temps above 160deg.

    The reason being is that the XS core flow a ton more, and will reduce flow to the engine substantially if you seperate the manifold path from the IC path. In this case, I highly recommend opening up the path, so that you can get full pressure to the XSCooler, and in turn a much more effective intercooler temp.

  8. #8
    My son (mohawk man) jeffsntx's Avatar
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    Mark, the diagram is showing an aftermarket I/C. Is 3/8 also a good starting point for the OEM intercooler as well? I was going to run a dedicated line for the intercooler where the Jetworks was plumbed on my 2 stroke set up.

  9. #9
    Hydrotoys's Avatar
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    If you are running the stock IC then use a small amount of 3/8" line (to duplicate the SD yellow restrictor) then step up the rest of the way with the large 3/4" line, and you should be okay. If it STARTS as a 3/8" supply, that might be perfect. Just hook in your large line to the IC, then manifold, then your standard 1/2 and 3/8" pissers.

    To check it on the water, put a oil pressure gauge temporary on your dash, and tee it at the inlet water on the IC. You want around 35psi on that opening at WOT.

    You DON'T want over 15psi on the engine open loop, if you are following the stock SD setup.

  10. #10
    JFizzleJR's Avatar
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    After finally experiencing my conversion ski run right I have a few questions regarding the open loop temp control.

    Would having more than 15 psi to the engine cause the temp to fluctuate 40į+ with the smallest adjustment on the ball valve? Is there any mod that can be done to better help control the fluctuation before the engine has been running for a while? Any mastermind have input on how to implement a thermostat in the open loop system instead? What exactly are the advantages of the ball valve?

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