1983 308 gts-qv Engine Compression test results | FerrariChat

1983 308 gts-qv Engine Compression test results

Discussion in 'Technical Q&A' started by rob58, Mar 25, 2022.

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  1. rob58

    rob58 Karting

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    Robert Orris
    #1 rob58, Mar 25, 2022
    I am looking at a 1983 308 gts-qv with 85,000 miles on it. The below figures are what the dealer gave me for the compression test results. Can any one read this? Are the results good, or bad, or somewhere in the middle? Please advise. Thank you all.

    1- 164 2- 165 3-155 4- 180

    Front

    4- 170 3- 150 2- 155 1- 175
     
  2. jcurry

    jcurry Two Time F1 World Champ
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    #2 jcurry, Mar 25, 2022
    Compression test or leak down? If leakdown is the basis 200? Engine hot or cold?

    Also, if leakdown where is the leak, i.e. rings, intake valves, or exhaust valves?
     
  3. rob58

    rob58 Karting

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    #3 rob58, Mar 25, 2022
    Not sure checking. This may take some time.
     
  4. rob58

    rob58 Karting

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    #4 rob58, Mar 25, 2022
    It was a compression test. Not sure if the engine was hot, or cold.
     
  5. flash32

    flash32 F1 Veteran

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    #5 flash32, Mar 25, 2022
    Ideally in general 10 percent tolerance between highest and lowest readings ..you have a few out the range ..





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  6. rob58

    rob58 Karting

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    #6 rob58, Mar 25, 2022
    Ok, is this measured in PSI, is that what these figures are? What does this mean, will the engine run poorly?
     
  7. flash32

    flash32 F1 Veteran

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    #7 flash32, Mar 25, 2022
    Yes PSI ..since they are not that off you may not notice the power reduction and /or probably won't have misfire or rough idle ..but that is what low compression (uneven compression does)

    The first noticable would be a misfire or a reduction in power on lower gears

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  8. flash32

    flash32 F1 Veteran

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    #8 flash32, Mar 25, 2022
    It is important to understand that many things can affect a compression test .. if a car hasn't been driven sometimes a ring gets stuck and then with some heat cycles it frees up and compression goes back up

    This is the first test ..the next thing would be to do a.leak down test and confirm issue ..and see where air is leaking into .. is it the valves , rings etc

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  9. flash32

    flash32 F1 Veteran

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    #9 flash32, Mar 25, 2022
    Even operator errors come into play .. were all butterflies open fully .. battery charged and kept full while doing test .. allow time for starter to cool off etc

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  10. rob58

    rob58 Karting

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    #10 rob58, Mar 25, 2022
    Wow!! This is all great information, and very helpful. I'm getting an education here.
    Thank you.
     
  11. wmuno

    wmuno Formula Junior
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    #11 wmuno, Mar 26, 2022
    As stated above, the engine should be warmed-up, the throttles wide open, and the battery fully charged. If the compression test was done by an experienced mechanic, the results should be valid. With the highest value being 180psi, the lowest values should all be above 162psi. Three cylinders fail. A leak-down test can tell you if the problem is with the rings or the valves.
     
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  12. johnk...

    johnk... F1 World Champ
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    #12 johnk..., Mar 26, 2022
    Bottom line. Those are not numbers which would give me confidence.
     
  13. Extreme1

    Extreme1 Formula 3

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    #13 Extreme1, Mar 27, 2022
    If the car hasn’t been driven regularly, I would put 50 miles on it and have them do another compression test.

    Test it with the engine hot or warm.


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  14. rob58

    rob58 Karting

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    #14 rob58, Mar 27, 2022
    Thank you all very much! I will take this advice and drive the car and have a retest. I appreciate all your comments.

    Regards
     
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  15. Extreme1

    Extreme1 Formula 3

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    #15 Extreme1, Mar 28, 2022
    Post the new readings if you can.


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  16. radlu

    radlu Formula Junior

    Jun 6, 2005
    411
    #16 radlu, Apr 6, 2022
    Sounds like an engine rebuild is in order.
     

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