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  1. #1
    quadzilla's Avatar
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    Question 1300 Pistons/Compression..??

    Hey Gentlemen..

    Have a couple of questions regarding my 05 Build..??!!

    The Story So Far:.

    My motor is now assembled back together with a Fercho 3 degree key, and VF3's.
    (OH.. went with pulling the motor out option to install these parts.. glad i did..!!)

    So the motor is back in the hull.. with my cut for 150 Riva stock head.(03-04 head)
    Unfortunately it was only showing 135-135-130 when i compression tested it..(Snap-On gauge)
    So off it came to get re-cut.. there was .012 left of the lip, this is now down to the squish band..

    On reassembly this afternoon with a New Yamaha head gasket i'm now getting 143-143-138.???
    Will check the squish clearance tomorrow..
    Now i'm certain if i go with one layer of gasket I'll get near or on the 150 mark.. (not keen on the one layer idea though)

    Now for the questions:.

    Firstly from a little bit of searching previous posts/threads it seems the pistons changed to forged from 05 onwards..?

    Also from looking at boats.net the part numbers vary between all the EFi ski's..??

    A piece of info that is likely important is my 05 was showing 127-127-125 compression before it got tore apart..(same Snap-On gauge)

    What i'm wondering is.? Are the pistons and cylinder head's different between the model years..???
    i.e Power Valve and Non Power Valve..? (aside from the forged pistons)

    Is it possible the earlier 03-04 pistons had a slightly larger(raised) dome and larger combustion chamber..??

    Does anyone know the cc's of each of the EFi heads..?? so 03-04's then 05 onwards..??

    Now i could go get my 05 head cut if that is whats required..(i'm looking to keep all the stock parts in hand should i want to sell it)

    Finally what would i be losing out on by staying at the compression as said above Vs the 150psi i was looking for..???

    One thing that comes to mind is a little bit of a safety margin due to the advanced timing..???

    OK Guys looking for your thoughts and idea's on where i should go from here..!!

    Gerry


  2. #2
    2000 GPRXP 4tec shooter98xpl's Avatar
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    7 psi is not going to make that much of a difference. Your fine where your at. Its the squish you want to make sure your not tight. Other than that, I'd leave it be where its at.
    I know Group K can mill your head further and open up the squish band area to accomodate the squish angle. But it runs $150 or $180, I can't remember off hand.
    SHOOTER

  3. #3
    quadzilla's Avatar
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    Lightbulb ?

    Hey Shooter..

    The only problem with using Group-K would be the 10,000+ mile round trip..

    Since i'm in the UK..

    As i said I'll check out the squish tomorrow.. didn't have any solder with me today..

    Any idea what clearance the squish band should be at..???

    Gerry

  4. #4
    quadzilla's Avatar
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    Question ????????

    Anyone..??

  5. #5
    mtrager's Avatar
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    My single pipe is 10 less in the back and it is very fast.

    Did lowell cut your head? Also I never get accuate readings until i put some hours on the motor.

  6. #6
    African-American
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    I assume u just got the cylinder head milled locally.

    I think Jim does a few extra mods to the head, besides just milling the base.

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