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  1. #1
    SJ-(KY)'s Avatar
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    Need to know Stock compression? 44cc compression? and 42cc compression?for a Ultra150

    Trying a set of heads out an unfortunatly I was in a rush an forgot to check stock compression in the motor b4 I put a new set of heads on... I feel the compression might be a tad low since there reading 1cyl 125.. 2cyl122.. 3cyl125 after installing the heads that were supposed to be somewhere between 42cc an 43cc... This was on a cold motor with the throttle open... Figured if I got an idea of stock an 42cc compression ratios that would tell me the heads wernt cut enough or I have some tired rings that need replaced .. Btw when u guys measure the cc's of one of these heads im assuming you measure with a spark plug in with the liquid up to the band of the head?


  2. #2
    jonny5's Avatar
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    stock is around 125psi 43 cc might get ya 130-135 42cc about 145 depending on heads,

  3. #3
    SJ-(KY)'s Avatar
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    Great..... :-/.. Sounds like I'll be freshening up the top end next week.... Thanks Jonny.. Still gonna try to gps some tonight since the humiditys down to around 38% an see what happens..

  4. #4
    jonny5's Avatar
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    I would put the stock heads on too to compare. The cut ones might not have been cut right and could do more harm then good. Because if the squish is down then that will advance the timing some so run 91 octane at least. Just because the compression is 125 doest mean you top end is done. How many hours.???

    I bet the heads are the problem.

  5. #5
    SJ-(KY)'s Avatar
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    Damn this thing ran strong as hell tonight in this good air.... Went a best of 69.6.. Yeah I think im gonna throw a stock head on one of the cylinders an see what it says.. Also after my machinest cut the heads down to lets say 42.5cc he machined the band back in the head an lighly radiused the squish area so now that I think about it that could be my problem....

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