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  1. #1

    1300 cylinders on a 800cc 66e GP800r?

    I'll be rebuilding a 66e soon. One of the pistons self destructed. Cylinders are already sleeved.

    I was told that I could use pistons from a GP1300R and gain 50cc or so in displacement and still be within range of the stock jetting.

    A few questions:

    1) Since my cylinders are already sleeved and need to be re-sleeved, can I simply resleeve with GP1300R sleeves and use the associated pistons

    2) The 66e is a PV motor - does the displacement size change the porting or PV requirements?


  2. #2
    Fat Man, Little Boat Region8Ultra250X's Avatar
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    the 66E and 66V have different port timing

  3. #3
    You may not need to resleeve.
    ProX have oversize pistons for the 800/1200 GPR's.
    Sizes available are 0.5 & 1.0 over std.

  4. #4
    These are already sleeved.. My understanding was you could increase displacement on these skis by using the 66v (1300 cc) cylinder.

  5. #5
    You could increase the displacement but not necessarily the power.
    66E 800 cylinders produce 60HP per cyl.
    66V 1300 cylinders produce 55HP per cyl.

    There's possibly enough meat on your existing sleeves to bore the cylinders to 84mm (1300) & take advantage of the extra porting the 66E cylinder has.

    I've not heard of it being done. Maybe someone else can pitch in here.
    You'll also need to have the head & head gasket recut.

  6. #6
    That's what I'm reading - that I'd need to adjust the head or perhaps take a 1300 cylinder and cut off one cylinder.

    Apparently the 66e exhaust is somewhat restrictive and may be the bottleneck...

    As this is looking more complicated than simply an overbore or cylinder swap, I'll likely decline..

  7. #7
    Chrisrokc's Avatar
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    Yea, you will want to skip on the 1300 cylinders and use the 800 cylinders. The 800 cylinders will make more power because of the port timing. What I would do is have the 800 cylinders bored out. Then you will actually gain something.

  8. #8
    Happily Self-Employed WFO's Avatar
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    ... and no, the jetting will not be the same with a 84mm vs a 80mm piston, plus the head will need to be re-cut

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