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  1. #1
    lownrangr's Avatar
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    fired up the xp today

    so with a new top end and new fuel system done i was able to get it started. I have a couple concerns. After the top end my compression was 170 and 160 psi. I have a novi head and one of the domes is dinged up kinda bad. I don't remember for sure, but i think i swapped around the domes but the compression numbers stayed the same in each cylinder. Question #1, is the 10 psi difference something to be concerned about? This will be a race boat and i was hoping I'd get even compression numbers after the top end. Question #2, will 93 octane be ok to burn? Thanks.


  2. #2
    Petron's Avatar
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    Quote Originally Posted by lownrangr View Post
    I have a novi head and one of the domes is dinged up kinda bad.
    Are you referring to similar item no. 19?

  3. #3
    lownrangr's Avatar
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    kind of yeah, but it's not a stock head.

    It just bothers me that my compression #'s aren't close. Grrrrr

  4. #4
    96XPSS's Avatar
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    Check your squish. This will conform if it will live on 93. No pipe right?

  5. #5
    lownrangr's Avatar
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    i have a spec II

  6. #6
    96XPSS's Avatar
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    I bet the 160 is the rear cylinder? 170 is borderline on 93. The difference between the two is ok. Check your squish...

  7. #7
    lownrangr's Avatar
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    ok i'll check the squish and report back. thanks for the help! And yes, the 160 is the rear. What does that mean? No need to sugar coat it!

  8. #8
    96XPSS's Avatar
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    Spec II's love to eat the rear pistons...lol So that cylinder will always be lower in compression due to the previous seizures. Unless you bore and clearance both cylinders, then they will be the same.

  9. #9
    lownrangr's Avatar
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    i don't think i'm doing it right, but the squish gap i'm getting is about 0.068''. Seems kind of high.

  10. #10
    96XPSS's Avatar
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    Bend your solder in a "Z" except at 90 degree angles, with each section about 1.5" long. Stick the first through the spark plug hole and and when you get the length right you will be able to feel it touch the cylinder wall. Lift the solder til it touches the top. Insert another and get both front and rear over the piston pins. It will take a little maneuvering, but when you get both held in one hand, flush with the top, use the other hand to hit the starter and bump it over.

    Give me all four numbers front to back and we'll see what you have.

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