News

How do these compression figures look?

Discussion in 'Technical Q&A' started by jakermc, Jan 21, 2004.

  1. jakermc

    jakermc Formula 3
    Owner

    Jan 17, 2004
    1,778
    Palm Beach, FL
    Full Name:
    Rob
    '95 F355 GTS:

    200 198
    185 195
    200 205
    200 200


    Any reason to worrow about the 185?
     
  2. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,969
    Maybe. Question, was the engine good and warmed up (full normal operating temperature*) at the time of the compression check? If so, then cylinder 2 is marginal. If not, have it redone with the engine good and warmed up.

    *You might consider a nice romp through your favorite back road to blow the carbon out before arriving at the mechanic to check the compression.
     
  3. jakermc

    jakermc Formula 3
    Owner

    Jan 17, 2004
    1,778
    Palm Beach, FL
    Full Name:
    Rob
    This is for a car I am looking at buying. The test was done by the Ferrari dealership. I always understood that the variance between cylinders was more important than the absolute number. Is the same true here? What are the rules of thumb I should go by?
     
  4. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    I've always been told a 5 - 10% range is within the bounds of being reasonable. 185 to 205 is therefore at the limit of this. To Mitch's point, ask what the car's temp gauge read when they did the test (again, I'd look for 185 degrees or so).

    Why not tell them you are a bit surprised and ask for a leakdown test (again, on a warm engine)? This will educate you (and the dealer) as to whether there's a problem [e.g., if most cylinders are 4 - 7% and one is 12% or higher] and they should be able to tell you the source of the issue (valves, rings etc) by listening for the source of the escaping air.
    HTH
    Philip
     
  5. Dino

    Dino Karting

    Nov 3, 2003
    116
    San Diego
    The leakdown test (especially on the '95) is more critical than the compression test, although both are prudent. It will alert you of the 'valve guide issue' i.e. compressed air is inserted into each cylinder and 'leaking' from the valves is measured in percentages. Leakage over 10 percent is generally accepted as problematic. All independant F dealers are aware of this test and it should be done before purchasing any 355. The first 2 355's I looked at ('97s) both failed the leakdown, which is why I went with a '98. Best of luck.

    Dino.
     

Share This Page