Results 1 to 10 of 10

Thread: Compression test

  1. #1
    steve_35 Guest

    Compression test

    What is the right pressure for a 3.5 efi /discovery motor compression test v8


    I have had it checked and they are around 120psi

  2. #2
    Join Date
    Sep 2006
    Location
    United Arab Emirates
    Posts
    496
    Total Downloaded
    0
    Anything around 130-150 is considered okay in my book with a wet compression test.
    120psi...I would not be so concerned as long as you didn't have one or two pots showing less than 100psi on a wet test.

  3. #3
    Join Date
    Jan 2010
    Location
    Newman WA
    Posts
    889
    Total Downloaded
    0
    Static compression is subject to your cam timing/duration overlap ,and very affected by the amount of air you let in !(I run 12:1 in one of my engines static , but with a fair bit of overlap the Dynamic comes down to 9.8:1 Seen many people to a Comp test without opening up the throttles fully , they get a bit disappointed then. Make sure all plugs are out and the throttles is wide open and use a positive sealing Comp guage , none of that push on stuff !!

    Is the 120 PSI a wet or dry figure ?

  4. #4
    Join Date
    Jan 1970
    Location
    Dalby
    Posts
    4,011
    Total Downloaded
    0
    Instead of starting a new thread I'll just add to this one.

    Does anyone know what the compression should be for a 8.13:1 3.9 V8?

    I have read online and found anything from minimum 120psi to minimum 150psi.

    RAVE doesn't say anything.

    My values were 4x155, 2x150, 2x160 psi.
    So they are all close in value. I'm assuming all is fine.

    The test was done with the motor at operating temp (I have the burns to prove it), no air filter and the throttle wide open.

    220K on the clock.

    I was going to replace the head gaskets due to the coolant leaking down the front of the block but if the compression is fine I won't bother.

  5. #5
    steve_35 Guest
    My mechanic said 150 - 170 is spot on

  6. #6
    Join Date
    Jan 1970
    Location
    Dalby
    Posts
    4,011
    Total Downloaded
    0
    Thanks. I had it in my head that 160 is good. So that answers that.

  7. #7
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    13,981
    Total Downloaded
    0
    Mine was 150 immediately after rebuild and is 145-150 after 100KK.

    I think 170 would show a lot of carbon and be in need of an Italian tune up.
    Regards Philip A

  8. #8
    Join Date
    Jan 1970
    Location
    Dalby
    Posts
    4,011
    Total Downloaded
    0
    Philip was that done at operating temp, no air filter and open throttle?

  9. #9
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    13,981
    Total Downloaded
    0
    Full throttle yes , hot yes .
    Air cleaner removed no.
    My entire inlet system has only 11 inches of water restriction at full throttle. At light throttle, restriction is not measurable on a Magnehelic gauge. If you went to the extent of removing the air cleaner , why not the MAF, then why not the throttle assembly?
    Regards Philip A

  10. #10
    Join Date
    Jan 1970
    Location
    Dalby
    Posts
    4,011
    Total Downloaded
    0
    They were just the instructions in the box. This is the first compression test I've done myself but I get your point.
    The instructions actually said to make sure the filter was clean or remove it if not.

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!