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compression. what should it b on this motor

Posted by spic21, Dec 7, 2010

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  1. spic21

    spic21 Proven Member

    238
    0
    Joined May 14, 2010
    albany, Louisiana
    I have a miss from what I believed to be fowled plugs because of my car running very rich. To the point that I am blowing black smoke out the exhaust. Also I had a bad boost leak that was coming out the valve cover so when I changed plugs I figured id do I compression test. So I pulled the plugs and mpi fuse along with coil to do test. When I first started test I was only getting 70-80 psi on each cyl. So I did a wet test and got 120 ish. Then I realize my dumb as* didn't remove the boost tester so I wasn't getting air to compress, so I pulled it off and retested. I got about 140-145 on every cyl. They where only 4 psi from one another at max. Because I had already put oil in cyl I knew it wasn't a good test. So I retested a few hrs later and the most psi I got was 120. Then I did it again this morning and got the same thing. Highest cyl at 120 lowest at 115. So I'm a little worried here, but also confused because there all so close to each other. I was using a cheap oreilly rental gauge. So I borrowed a very expensive comp gauge and leak down tester from the mechanic that does all the work on my cars at lot. And I will test it again tonight. I question is if I post all the internal part pistons, rod, head gasket can anyone tell my about what compression ratio I should be at. The motor was built by me and a very good friend of mine with his dad who build lots of race motors. The only problem is it was done 6+ years ago and no one can remember if we were lowering compression or not. I'm going to scan all my paper work and post it so maybe ya'll can help me on this. Only thin different is I blow a head gasket 4 or so years ago and replaced it with a cometic head gasket and all I remember about it was it was rated for up to 30 pound of boost. This is all the paper work i have. Also this motor doesn't even have 1000 miles on it since the build. If i do have an internal problems im probably done with this car and im gonna just part it out or sell it as is. If you need or would like to know anymore info its all in my profile(might have added one or two other things but that basicly it)

    Head is stock with parts i posted and 3 angle vavle job.
     

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    Last edited by a moderator: Jun 5, 2014
  2. BogusSVO

    BogusSVO Proven Member

    5,715
    278
    Joined Jul 1, 2009
    Pensacola, Florida
    without the Head cc numbers, and what the piston to deck measurement is.. your CR will be a guess
     
  3. spic21

    spic21 Proven Member

    238
    0
    Joined May 14, 2010
    albany, Louisiana
    i kind of figured that. want to guess? im really at a lost here and dont know what to do but pray that i get a better reading when i do it tonite with the knew gauge
     
  4. spic21

    spic21 Proven Member

    238
    0
    Joined May 14, 2010
    albany, Louisiana
    Just did another test with a compression gauge I know is good. I got between 170-180 psi on all cyl. Is I know now it's good. Now I was wondering why so high. Shouldn't it be about 164. I'm guessing it's ok here though?
     
  5. 1990AWD

    1990AWD Supporting VIP

    1,464
    16
    Joined Apr 27, 2009
    Langham, SK, Canada
    yes your good. the higher the better. (unless you had some n/t pistons in there or something LOL)
     

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