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  1. #1

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    why does the gp800 tun such low compresion

    i kinda curious why the gp 800 runs such low compression . mine had 130psi which im told is factory. to me this seems pretty low my 750 in my x2 rubs 175psi on pump gas (95-98 octain from the pump here in nz)with out a problem . i know the 800 puts out alot more power but the low compression has me wondering . would it be safe to bump it up a wee bit say to around 150psi


  2. #2
    qbzonk's Avatar
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    besides being required to run higher octane fuel, what type of changes do you expect to get by bumping compression?

    Even if u manage to squeeze out a HP or two, it will be negligable in performance gains.

  3. #3
    cheatin' piston popper addicted's Avatar
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    Doesn't the position of the power valves effect the comp #'s?

  4. #4
    cfgp927's Avatar
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    compression

    I have run as high as 165 on 91octane pump gas and as high as 180 on a mix of 100 Av Gas/91 unleaded. i presently run 150 on my wife's XL800 with 87 octane and oil injection. The other two compressions were with oil/gas premixed at 40:1. This was on stock bore 66E motors.

    Valve position will change compression. Always check with the valves in the down position. It will vary about 10-15psi in the up position.
    Mike

  5. #5

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    thanks guys ive got gas power valves and they were when i did the compression test . i am going to leave the compression at the 130 mark for now i was just curious thats all . in new zealand we have 95 and 98 octain avaible from the pump and i can get rave gas if i feel like a 15min drive .

  6. #6
    cfgp927's Avatar
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    compression

    W-nut....is this Braedon? The picture of the motor you posted earlier looks like some you sent me of your ski.
    Mike Stackhouse

  7. #7
    Moderator RX951's Avatar
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    Remember to check compression with the throttle wide open.
    130 psi is stock compression.
    You can safely run 150 on pump gas. But do not go below 91/92 octane.

    Proper Engine Compression Testing
    http://www.greenhulk.net/forums/showthread.php?t=9411

  8. #8
    Mongoose's Avatar
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    Also, you must remember that the 800 jugs are more radically ported than the 1300's.
    In fact-sticking the 800 jugs on a 1200/1300 is like having a fairly radical port job done.
    The difference is THAT much!

  9. #9

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    Quote Originally Posted by w-nut View Post
    thanks guys ive got gas power valves and they were when i did the compression test . i am going to leave the compression at the 130 mark for now i was just curious thats all . in new zealand we have 95 and 98 octain avaible from the pump and i can get rave gas if i feel like a 15min drive .
    If you are comparing the Octane rating to the US ones they are different to the rest of the world. ie in the UK we get 95 and 98 RON octane at the pumps which equates in the US to 91 and 93, I think.

    But ours is the same price as liquid gold ie approx $8 to the US Gallon

  10. #10
    Quote Originally Posted by w-nut View Post
    i kinda curious why the gp 800 runs such low compression . mine had 130psi which im told is factory. to me this seems pretty low my 750 in my x2 rubs 175psi on pump gas (95-98 octain from the pump here in nz)with out a problem . i know the 800 puts out alot more power but the low compression has me wondering . would it be safe to bump it up a wee bit say to around 150psi
    Here is a excellent article on the 800 yes you can bump it up ! and it will increase performance quite a bit !!http://www.groupk.com/y800gp.htm

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