Results 1 to 7 of 7

Thread: Compression readings on early S

  1. #1

    Compression readings on early S

    What are considered good compression readings for a
    1972 911S?

    I got the following readings a year ago:

    45 45 45 35 40 45

    thanks for any help here,

    Mark Sutherland

  2. #2
    I'd always hear that the numbers themselves weren't as important as how close together in number each cylinder is. This because different compression gauges give different readings. Another informative test is a leakdown test. Did you have that done? Hope somebody else chimes in...because this about all I know.

  3. #3

    Compression readings on early S

    Hi Mark,
    Your compression readings are low, but just to make sure we're in the same ballpark:

    Battery charged
    All plugs removed
    Throttle open
    Engine warm
    Crank engine and record the highest comp. reading after about 9 compression strokes

    I believe you should be around the 130-150 psi range on all cylinders (it's been awhile since I did this on an "S").

    If your readings remain about the same I would suspect your piston rings are rusted in place. You can also do the perfunctory "squirt oil in the cylinder and take another reading" test as well.

    The good thing about compression readings of 45 45 45 35 40 45 is that they're all even :-).

    Let us know if there's life in the S.

    Sherwood Lee

  4. #4

    Add one hundred ... i sure hope!


    I am assuming then that my readings were
    145 145 145 135 140 145

    The engine runs real strong and I think my mechanic would have informed me if I was 100 psi off!

    Just in case, I will check with him and thank you for your reply.

  5. #5

    The leak down test

    Can someone elaborate on the leak down test. By it's name it sounds as if you pump air into the chamber and see how long it takes before you lose x% of the pressure.

  6. #6

    Re: The leak down test

    In a nutshell, that's it. Test shows how tight the engine is by how fast it leaks air. A diagnostic test that goes hand in hand with a compression test. A good mechanic can often diagnose if there is a problem, and it's likely cause by using both compression & leakdown tests. Valves, rings, etc.

  7. #7

    Re: The leak down test

    The "leak down test is the most efficient. The "acceptable" % is 12%. I watched my mechanic perform it on my '73S. My car was <2% on 3 cylinders, and <1% on the other 3. Anything under 3% is what mechanics call impressive.

Similar Threads

  1. AFR Readings (LM-2) - Idle speed vs. Partial load
    By TEC69E in forum Technical Info
    Replies: 9
    Last Post: 02-03-2011, 05:59 PM
  2. what should compression readings be 69 911s?
    By blucille in forum General Info
    Replies: 6
    Last Post: 05-25-2005, 07:07 PM
  3. compression
    By 72starga in forum Technical Info
    Replies: 4
    Last Post: 07-24-2003, 03:29 PM
  4. Dyno readings
    By A67911S in forum Technical Info
    Replies: 7
    Last Post: 11-11-2002, 12:09 PM
  5. High compression test readings
    By Baddger74 in forum Technical Info
    Replies: 2
    Last Post: 02-21-2002, 03:30 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.