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Thread: 69 E Compression

  1. #1

    69 E Compression

    My mechanic did a compression test this week and reported these results...1) 148, 2) 147, 3) 148, 4) 149, 5) 145, 6) 150. He also said that compression on this motor should range from 128 to 156. Hoping someone can opine on these numbers and range as well. Thanks in advance, much appreciated.

  2. #2
    Where was the test done? At which altitude? this article on Pelican is very informative regarding compression numbers, https://www.pelicanparts.com/techart..._rebuild-2.htm

    From the article --- A standard compression reading of about 150 psi at sea level in Los Angeles would measure significantly less in the surrounding mountains. For example, at an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.

    Compression Test Altitude Compensation Factors
    Altitude Factor
    500 0.987
    1500 0.960
    2500 0.933
    3500 0.907
    4500 0.880
    5500 0.853
    6500 0.826
    7500 0.800
    8500 0.773

  3. #3
    Senior Member NZVW's Avatar
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    They look pretty tidy

    The 128--156 range is based on the altitude and temp when tested.
    150+/- being at sea level and decreasing with elevation.
    There is a Table that is used to calculate your elevation but I am damned if I can find it.

    Mark

    I never came 1st in a typing race lol

    Just as a foot note,, a leak down test is as important.

  4. #4
    Guys, thanks for your input. I'm in St Louis so very at or near sea level.

  5. #5
    Senior Member
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    What would the comparable results be for a 69 S??
    1969 911S Targa
    1970 911S Coupe
    1973 911T w 3.2
    1972 Alfa GTV 2000

  6. #6
    Due to 'S' cam overlap probably slightly less, leakdown is much better method. No variable due to battery condition, starter strength, or number of cranks. Can't give you exact number since we don't use compression tests.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  7. #7
    Senior Member beh911's Avatar
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    Quote Originally Posted by Frankr View Post
    What would the comparable results be for a 69 S??
    My 93k mile 69S with its 49 year old unrebuilt engine was 135-140 across all six last time I checked. 1000 feet asl.
    To me consistent with age and the valve overlap comment from Ed.
    1969 S Coupe #761
    Early S Registry #1624

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