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  1. #1
    Mongoose's Avatar
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    Help me decide! 1300 or 1390

    Bought a 2001 project GPR with 120 hours on it.
    I have decided to go down the road of building a reliable hard hitting surf ski with it.
    It already has the Pro-tec wake up kit, and it's a bit quicker out of the hole than a 06 efi, but not by much.
    Should I go with 1300 cyls and gas valves-Much easier to source and fit over here in the Uk, or should I just send the top end to GroupK?-Major headache from over here, but possible.
    I think what im trying to ask is-Is the 1390 going to hit out of the hole that much more than a 1300 -enough at least to warrant the extra?(hassle-not cost). I don't mind spending if the reults are going to be there!
    Has anybody got any accelaration data they can post or pm?
    Thanks again.
    P.S-im so concerned about holeshot,Im even thinking bout getting an Xp instead!!, but probably won't!


  2. #2
    TRIPLE PIPES ARE 2-STROKE TURBOS allcool's Avatar
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    Why not go 1390 With power valves?

    allcool

  3. #3
    Mongoose's Avatar
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    Quote Originally Posted by allcool View Post
    Why not go 1390 With power valves?

    allcool
    I think that would be better, but I don't know of any other company other than group k that offer a 1390 set up.

  4. #4
    Me Hahn and Joe H204YOU's Avatar
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    Ben Herman in the tuners corner can fix you up.A 1390 with power valves will have a massive hit down low,and can spin a 25-p dynafly for some good top end too!

  5. #5
    TRIPLE PIPES ARE 2-STROKE TURBOS allcool's Avatar
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    You can get 1390 pistons from group k. Although Lowell might have some also.

    Anyone that bores and plates in the UK should be able to do the job once you have the pistons. In addition, you will need at the least some mild porting to match everything up.

    iirr someone on our forum from the UK just was thanking one of the forum tuners for helping them with info for a machine shop in the UK to get some work done... look for it in some past threads.

    allcool

  6. #6
    Mongoose's Avatar
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    Quote Originally Posted by allcool View Post
    You can get 1390 pistons from group k. Although Lowell might have some also.

    Anyone that bores and plates in the UK should be able to do the job once you have the pistons. In addition, you will need at the least some mild porting to match everything up.

    iirr someone on our forum from the UK just was thanking one of the forum tuners for helping them with info for a machine shop in the UK to get some work done... look for it in some past threads.

    allcool
    Looked into it-nobody over here re plating cyls.-plenty of machine shops also, but ne real experience in porting our skis.

  7. #7
    YudLuz2's Avatar
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    Quote Originally Posted by Mongoose View Post
    I think that would be better, but I don't know of any other company other than group k that offer a 1390 set up.
    Hey Mongoose
    I would be happy to help you a 1390cc setup with power valves. I usually
    carry the core cylinders and valves in stock, so it wouldn't be nessary to
    send me any parts if you are wanted to save on shipping. l can supply the head too. I have done a few for people overseas and I'm getting ready to send a 1390 triple kit to someone in Sweden. I dropped one in a single piper last night. I use the Group K pistons and usually have Lowell to custom cut my heads to my needs. The 1390cc will accelerate harder than the 1300. It can be made to rev high like the 1300, giving
    it great accelerate and top speed. So you can get speed and acceleration and not have to give up anything. You can p.m. for pricing and details
    are email me. Thanks Ben

  8. #8

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    Quote Originally Posted by Mongoose View Post
    Looked into it-nobody over here re plating cyls.-plenty of machine shops also, but ne real experience in porting our skis.
    Jet Shed can get cylinders replated, if you need it done in the UK.

    But not sure if the know the 1390 setup ie AFAIK the boust port need porting as the bigger bore reduces its timing, the PVs need reradius, getting the correct comp ratio etc.

  9. #9
    Mongoose's Avatar
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    Quote Originally Posted by kevski View Post
    Jet Shed can get cylinders replated, if you need it done in the UK.

    But not sure if the know the 1390 setup ie AFAIK the boust port need porting as the bigger bore reduces its timing, the PVs need reradius, getting the correct comp ratio etc.
    They have no clue about porting a Yam (might be differnt with Sea doo)
    Rung them up, and i was told porting on the GPR's is not worth it, best to not bother.Kinda put me off even sending my cement mixer there!

    If they can't do it-fine-just tell me, but to come out with bollocks like that pisses me off-NO buisness from me!

  10. #10
    Chine Walker
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    Ben:
    Are there alternative pistons for the 1300 to 1390 kit? From what I've read Wiseco seems to be the only option; is there anything that's comparable quality to Yamaha's forged units?
    Does your conversion work with EFI, and if so will the mixture be relatively sorted out?
    Regards,
    jp
    NY.

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