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  1. #1
    Chine Walker
    Join Date
    Nov 2006

    Machining the head of a GPR 1300

    For those of you who have increased the compression of the 1300 '03 motor; is the head milled equally across the whole surface? I see in the shop maual that cyl #3 has a slightly lower comp ratio than cyl. 1 & 2. Is this achieved by piston shape or cyl. deck height? Different deck height would create an uneven surface for a one piece head wouldn't it?
    I'm looking to achieve only a slight increase; something in the 135-140 lbs at most. Reliability is paramount.

  2. #2
    SpeedJunky's Avatar
    Join Date
    Dec 2005
    #3 cylinder has a larger cc dome volume.

  3. #3
    The head would be machined evenly across all 3 maintaining the factory staggered compression. We can machine the factory head.

  4. #4
    Chine Walker
    Join Date
    Nov 2006
    Thanks Carl. As per our conversation I only want a small increase; definately under 140lbs. At this point would you suggest the EFI controller?

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