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308 Leak Down Test.

Discussion in 'Technical Q&A' started by Neilg, Apr 18, 2005.

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  1. Neilg

    Neilg Karting

    Feb 16, 2001
    241
    Accokeek, Md.
    Full Name:
    Neil Green
    #1 Neilg, Apr 18, 2005
    I was wondering if anyone has performed a leak down test on their 308, and if so, what air pressure (psi) is used to pump into each cyclinder to perform this check. I suspect I may have a faulty valve, but before removing the head (rear bank) I want to perform this test. Also, if you know what percent differences I should expect to see (healthy engine) that would be great. Thanks in advance.
     
  2. ferrarifixer

    ferrarifixer F1 Veteran
    BANNED

    Jul 22, 2003
    8,520
    Melbourne
    Full Name:
    Phil Hughes
    #2 ferrarifixer, Apr 18, 2005
    The pressure is not too important.

    The test involves comparing compressor pressure from your supply, to residual pressure in the cylinder during the test.

    Typically, compressors in the workshop run at around 90-120 psi.

    It is important to have a large tank, and to keep air usage from the tank to a minimum while doing the test, as if the tank volume/pressure goes up and down from compressor cycling, without re zeroing the tester, you'll get misleading readings.

    Perfect engines will have less than 5% leakage to the crankcase (none to cooling/inlet/exhaust), and vary by only 1 or 2 % across cylinders.
     
  3. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    #3 pma1010, Apr 18, 2005
    One data point: my 77 gtb, three years ago:
    4 - 6% on all cylinders apart from one which was higher and leaking into the case (i.e., rings). Compression two years later was 185 +/- 5 psi. Stock cams.
    Philip
     
  4. Neilg

    Neilg Karting

    Feb 16, 2001
    241
    Accokeek, Md.
    Full Name:
    Neil Green
    #4 Neilg, Apr 18, 2005
    Thanks for the information.....
     

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