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  1. #1
    VdeKock's Avatar
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    GP1300r upgrade to 1390

    Is it possible to make my current ported non pv 1300, a 1390cc
    all the 1390 skis I see are power valve engines.

    Is GroupK still dealing with this kits?
    if possible I want to keep my own cylinders.

    A GPRSHO would be great but there aren't many donor engines around here
    or they cost a ton including trash hull.


  2. #2
    800AMSOIL4U's Avatar
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    http://www.wcporting.com/
    Talk to Kevin.

  3. #3
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    I'd fix your ski first, you have a ported ski doing 75. You should be doing 82-84. A bone stock GP1300r with nothing but a milled head, EJK, impeller, and jim's plate do 75 all day long.

  4. #4
    VdeKock's Avatar
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    Unfortunately I don't have glass smooth water, always choppy here....
    And I haven't seen much ported 1300 go over the 80's

  5. #5
    Prism's Avatar
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    The answer is yes. There will be some port modifications again after the cyls are bored. After the ports are corrected and chamfered again, they get sent out for replating. You will need the head and head gasket modified, and possibly clearancing the case. At this point it seems cheaper and easier to just buy a 4 stroke and mod it than doing the conversion. If you're really good with the hull setup and have the 1390 done, you should be as fast as all but the most brutal 4 strokes out there... not including the rare conversion you may run across. IMHO I've got too much already invested in my GPRs to chase the boost and start over buying thousands of dollars in FZR or RXP parts....conversion or non conversion. Like I said, a ported 1390 will keep up with all but the most serious 4 stroke non conversion skis. The only other thing is the chop conditions you mentioned.... a bigger hull is usually always faster in the chop. That's why Kawasaki is cleaning up at the pro level.

  6. #6
    Almost's Avatar
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    Quote Originally Posted by riick370 View Post
    I'd fix your ski first, you have a ported ski doing 75. You should be doing 82-84. A bone stock GP1300r with nothing but a milled head, EJK, impeller, and jim's plate do 75 all day long.
    Do you just sit around waiting to make a smart ass remark? You sound like "that dude", he didn't last around here that long before he got banned with his know it all attitude. Not everyone sets their ski up to chase speed. There are closed course setups and rough water setups and surprise surprise people run them. It doesn't make a lot of sense for some people to set their ski up for something they only run in(flat water) a small amount of time.

  7. #7
    OzarkYamMonster's Avatar
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    Well I am here to tell you I have yet to find the GP1300R that with just milled head, impeller change, Jim's plate do 75 all day long. No such thing. Even doing porting the engine with those other few mods ... won't get you to 82-84 GPS. It take advance timing ... reed changes .... intake grate changes ..... and a shit load of tuning! Then to get over 80 is very tuff .... ask me how I know.

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  9. #8
    Quote Originally Posted by OzarkYamMonster View Post
    Well I am here to tell you I have yet to find the GP1300R that with just milled head, impeller change, Jim's plate do 75 all day long. No such thing. Even doing porting the engine with those other few mods ... won't get you to 82-84 GPS. It take advance timing ... reed changes .... intake grate changes ..... and a shit load of tuning! Then to get over 80 is very tuff .... ask me how I know.
    I have seen them on here doin 75

  10. #9
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    There's skis on here doing 75 with just milled head, West Coast porting regularly has skis doing over 80 with porting without issues.

    It's all in the hull. Before my motor blew Duke said my ski had no issue getting to 71-72mph with a BONE STOCK engine and we were almost there, til the dealer blew it up. All that was needed was a little more plate angle and he was going to tweak the prop. I had TWO MONTHS of tuning in my hull, watching TV with a file taking thousands off my pump shoe, intake, or plate. Then having someone tweak the impeller for the perfect WOT rpm. You would think I was an engineer with all the super accurate rulers, levels, and other measuring tools I had to purchase. Not to mention a data logging tach and GPS which are tools you can not do without.

    If you think you can buy parts, bolt them on, and be done? That's why there's people doing 70 with milled heads and 75 with ported motors.. and the people that spend the time tuning can do 70+ bone stock, 75+ with just milled, and 80+ ported.

  11. #10
    OzarkYamMonster's Avatar
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    OK, I surrender .... I guess my time spent in the trenches was just a prelude for something not attainable. I have paid my dues to the speed gods ... and their rewards are slow in coming. My route to speed is time consuming & costly. Short of boring my engine ... there is nothing left for me to do. My now sits in a shop completely torn down awaiting a twisted crank repair & rebuild. I do know that if I was getting 75 GPS all day long on just a milled head & some bolts-on, this long journey would not have been necessary. But what do I know LOL

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