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  1. #1
    philip_gpr's Avatar
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    Machined OEM head - what squish do you end up with?

    If you machined an OEM GP1300R head to get to 150 lbs compression, what squish would you be at?

    assume just the head mating surface is being machined and you use both layers of the head gasket

    thanks, philip


  2. #2
    Mine is from .050-.055 philip, lip machined off..150 psi.

  3. #3
    Duke's Avatar
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    There are 2 or more different 1300 heads. Jim or Lowell could tell you exactly depending on which one you have.

  4. #4
    Happily Self-Employed WFO's Avatar
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    Plus, Lowell re-machines the squish band on his stock heads, so there would be a slight difference in a Jims cut head vs a Lowell cut head.

  5. #5
    philip_gpr's Avatar
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    ok thanks guys

  6. #6
    OLD # 7 IEGPR's Avatar
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    Mabey I have the worng info but I read somewhere a stock head with 30 tho cut off gives a good squish band.

  7. #7
    www.2-Stroke-Porting.com
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    Philip

    I cnc the head down to a 2-3 thou step. This leaves a 50-55 thou squish with 2 layer head gasket. I machine the base of the cylinders 15+/- thou, to true them up, and allow the use of a stock head gasket. This gives a 38-40 thou squish clearance.

    Hope this helps.

    Lowell

  8. #8
    fastkaz's Avatar
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    how much owuld you have to take off without taking from the cylinders to run 145-150

  9. #9
    www.2-Stroke-Porting.com
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    You can cut the "step" down to the squish band 30-33 thou and you will be close to the 145-150 psi. The problem is the stock squish band is cut at about 8* angle and the piston crown is close to 10*. You have a squish clearance close to 42 thou at the combustion chamber and a 50+ thou squish at the cylinder wall. Not Good for moving the fuel / air into the combustion chamber.
    The engine will run fine. Just not the most efficient combustion process.

    I have no idea why Yamaha did this. This is why I cut ALL squish bands on the '03 and later heads.

    Hope this helps.

    Lowell


    www.2-Stroke-Porting.com

  10. #10
    Chine Walker
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    Lowell:
    Do you find it necessary to machine the cylinder bases when the head is cut? If you where to cut a customer's head, should the cylinders be sent together??
    Regards,
    jp

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