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  1. #1
    novice duudu's Avatar
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    Gpr-sho conversion vs over-bore & stroker . Help me decide

    I`d like some help in deciding what course to take with upgrades for my 06 gp1300r.
    Right now the mods read : cut head, 4 degree keyway, power filter (k&n on stock airbox) , air baffles removed (arrestors ? ) , d-plate, ngk bkr8eix , freeflow exhaust and jetworks mod. Those are mods related to engine performance. The hull/handling got some upgrades too : 14/20 dynafly , jims ff plate , r&d double bar intake , extended/shimmed trim tabs ,leo`s 2 degree wedge and an extended steering nozzle.

    This has made my ski pretty playful but at times it can be a handfull . I`ve been to the fun side of 100km/h and to be honest it isn`t that fun to come off at that speed.
    A friend has a fzr sho in stock form and I got to do some comparison runs against him.
    My gp1300r is nimble , it can be flicked from side to side , it jumps waves and has a higher top speed. When going side by side , after 50km/h I start gaining and keep going noticeably faster. No gps speed though.
    The problem is it doesn`t get to 50-60 km/h quite fast enough . My ski has 3 main purposes : towing , wave jumping and maybe less than 30% of the time calm lake runs.
    It`s pretty good at towing in the sense that I`ve dialed the boat in where it doesn`t tail whip and keeps rpm constant and also great on calm water days but the problem is that it`s crap everywhere else.
    If the conditions are less than good/perfect it`s a nightmare. I have to dial the trim all the way down if there is any hint of waves on the lake or it will bounce me to the point of being dizzy , riding two-up makes it worse. On the sea it becomes unhooked almost instantly to the point I'm being given a run for my money by Sea Doo gtx`s .
    During wave jumping sesions it doesn`t have the holeshot I would like , it takes some time for it to react to throttle stabs and when it does it usually goes up rather than forward and becomes unhooked causing me to loose traction right before a wave and leading to me getting bubbly because the wave impacts right on my face.

    I`ve read a lot of threads about sho conversions but not a lot of info on holeshot and general behaviour . Also does this take away from the nimble aspect of the ski? I`ve ridden the sho and don`t really like the fact that it feels 200kg heavyer than the gpr.
    What I do like on the sho is the instant go. The gpr is spectacular when it holeshots , you can distinguish the phases (incipient hesitation, going up on the plane, acceleration from 40-50km to midrange , etc) , you have to "work" it , while the sho is just like an idiot`s tool , press the lever for instant speed , no fuss , no changing weight balance , no waiting, it just goes.
    What`s the general consensus , does porting , over-boring non pv cylinders and maybe stroking (since we are talking about under 7500 rpm) get you close to the 1.8l supercharged torque ? I would like to stay away from tripple pipes as I see they are quite labour intensive.

    Another aspect is cost . At 5-6 k for the sho engine , 1-2 k for ancillaries and another 1-2 k for fitting it to the gpr hull , without any tuning or upgrades is it worth it ?
    I can see an engine build for the 1300 going to 4-5 k but then again that pretty much covers it.


    Cheers and I hope I get some insight on this as I`m really not decided on what to do.


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  3. #3
    novice duudu's Avatar
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    I guess nobody that had both a conversion and a big-bore could spare a few minutes reply.
    I`m going with the overbore.

  4. #4

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    if it was me I would go with the sho, just because it a 4 stroke and less maintence and less thing to worry about.

  5. #5
    dlamazing's Avatar
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    Quote Originally Posted by duudu View Post
    I guess nobody that had both a conversion and a big-bore could spare a few minutes reply.
    I`m going with the overbore.
    sounds like you need a GPRXP! first off its faster stock on stock form compared to a GPSHO also if you wanna tow someone GPSHO is not the way to go that motor is verry heavy and sits in the water alot lower you will end up sinking your self towing lol also wave jumping the rxp motor holeshots verry nice for that! dont mess with the 2 stroke sell all that stuff and put it for your conversion project have fun

  6. #6
    philip_gpr's Avatar
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    let's see big bore motor makes something like 190 to 220 hp

    4 stroke SC motor using pump gas makes anywhere from 210 ro 375

    4 stroke will have more low end hp

  7. #7
    novice duudu's Avatar
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    Quick vid of the "BOUNCE" and holeshot .

  8. #8
    WATER WOODY's Avatar
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    Were is your life vest.....

  9. #9
    cigarlust's Avatar
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    Dem are some nice shorts too...

    I think building a GPRXP would get you what you want without dumping stupid money into the ski, the sea-doo power plant is very capable and reliable...

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