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  1. #1
    Chupacobra's Avatar
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    How Much Is Everyone Taking Off The 1200R Head To Reach 140-155

    I'm going to be cutting the head on my GP1200R. I was wondering If anyone know how much to take off to reach a comp of 140-155 range. I figured to just ask here instead of taking the time to do the math Thank you!


  2. #2

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    Bill is the guru to ask, he usually sells heads already cut.

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    Moderator OsideBill's Avatar
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    if you cut it to the squish band, you can get about 135 out of it. You have to cut into the squish band and reshape it to get 145-150

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    Chupacobra's Avatar
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    Any idea how far to cut? Thanks!

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    Moderator OsideBill's Avatar
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    Quote "up to the squish band"

  6. #6
    Chupacobra's Avatar
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    I was asking into the squish band

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    Moderator OsideBill's Avatar
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    basically when decking a head you dont want to cut into squish, cut up to it and stop. if you go past you risk hitting the head with the piston. measure the step subtract .003" and cut that much. the steps vary slightly from head to head, on average they are roughly 1mm or .040" but measure to be accurate.

    The best way to cut is to cut for CC, that is what dictates PSI. I developed a CNC program that cuts the deck, squish band and blends a radius into the dome. I cut once to an established depth then measure and adjust based on a formula I have worked out. took awhile to get things dialed in but now that I have acquired a tremendous amount of data I can them relatively quickly.

  8. #8
    Chupacobra's Avatar
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    Thanks a ton for all that info! I'll Give It a try!!

  9. #9
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    +1 on Bills advice and if you are going to do it yourself try experimenting with splitting the head gaskets and miking them and seeing how much it changes the compression. There is a lot of figuring you have to do and reshaping the combustion chamber as not to damage something.
    When you do get the head done and torqued down before you turn the motor over get some solder and bend it so you can put it through the spark plug hole and reach the side of the cylinder and turn the engine by hand the piston will squish the solder and you can mike it and get the squish. you will need to take at least 4 measurements per cylinder. the front and rear of the piston and side to side. you can add the 4 measurements and divide them by 4 to get the average.

  10. #10
    Chupacobra's Avatar
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    Thats a great idea, I was going to use clay but the solder seems like a much easier alternative.

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