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  1. #1
    night022's Avatar
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    OEM head milling compression results

    yesterday got my milled head back, he cuts 0,500 mm (0,0196850394 Inch) off.

    Compression before millling
    117 PSI (8,0 Bar)
    118 PSI (8,1 Bar)
    118 PSI (8,1 Bar)

    Compression after milling
    131 PSI = (9,0 Bar)
    134 PSI = (9,2 Bar)
    134 PSI = (9,2 Bar)

    all these measurement was done at 400m (1300ft) over sealevel, cold engine and WOT

    Is there a compression difference if i do the same test at sealevel?

    PS: 2007 GP1300R with 15 hours
    Last edited by night022; 08-28-2008 at 12:21 AM.


  2. #2
    txgp1300r's Avatar
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    Yes..think about it...sea level you got thick air, up high you got thin air....get the squish to about 45 thou and it will run good on pump gas(140-150 psi)

  3. #3
    night022's Avatar
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    Is there a formula to calculate this difference?

  4. #4
    Waveruiner pauladave's Avatar
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    I realise a bigger bang should give more power, but what other mods to carbs etc. are needed if the heads are milled to produce more psi? Is it just a matter of milling the heads, or are there knock-on effects. I know fuel choice is more critical, but what other changes are needed, and does the extra psi really give a major gain? I've a XL1200Ltd (p/v).

  5. #5
    o uncola o's Avatar
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    Quote Originally Posted by pauladave View Post
    I realise a bigger bang should give more power, but what other mods to carbs etc. are needed if the heads are milled to produce more psi? Is it just a matter of milling the heads, or are there knock-on effects. I know fuel choice is more critical, but what other changes are needed, and does the extra psi really give a major gain? I've a XL1200Ltd (p/v).
    ttt

  6. #6
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    Quote Originally Posted by night022 View Post
    yesterday got my milled head back, he cuts 0,500 mm (0,0196850394 Inch) off.

    Compression before millling
    117 PSI (8,0 Bar)
    118 PSI (8,1 Bar)
    118 PSI (8,1 Bar)

    Compression after milling
    131 PSI = (9,0 Bar)
    134 PSI = (9,2 Bar)
    134 PSI = (9,2 Bar)

    all these measurement was done at 400m (1300ft) over sealevel, cold engine and WOT

    Is there a compression difference if i do the same test at sealevel?

    PS: 2007 GP1300R with 15 hours

    .5mm is not enough, i took .8mm and got 140.

    the way its calculated is by dome capacity and any good engineer/tool maker should be able to do the calculations for the dome capacity to get you the comp and squish you want as long as they know what they are doing. I was told by someone well respected on here last night that you can ask someone like Lowell for 153psi and your head will come back with 153, its that exact if the person doing it knows how to do it.

    Ask Water Woody about how altitude affects compression etc... as he lives high up in the mountains somewhere and knows first hand how it plays a part in ski performance.

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