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  1. #1
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    Hemi compression test write-up?????

    Does anyone have clear leads or links to a step guide compression test and it's "good" results anywhere?

    I've tried the search function with no luck.

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  2. #2
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    Why do a compression test? Leakdown gives you much more info. Even at 50% motors still run good. Our race motors are usually about 4%.

  3. #3
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    Quote Originally Posted by electjohn View Post
    Why do a compression test? Leakdown gives you much more info. Even at 50% motors still run good. Our race motors are usually about 4%.
    Do you have specs, guidelines, or numbers for said test on a good standing hemi?

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  4. #4
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    iirc good compression is 185-190


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  5. #5
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    My motor is around 8% in all cylinders. That's what it was new, and still is now with 150k. The actual number doesn't matter (within reason) so much as all cylinders are the same.

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  6. #6
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    Hemi compression test write-up?????

    Also, I had 185-190 on all cylinders, still had head gasket failure on two. Pumped air into the cylinders and heard it in the coolant tank.

    This is why a leak down is much better

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  7. #7
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    Hemi compression test write-up?????

    I had cylinders come in great on compression. Did a leak down and all was within 4%. Still had a bad ring in a new build and it had scored the liner and had less than 2000 miles on it and was no noise / air comming from anywhere so leak down and compression test are not always a tell tale sign


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  8. #8
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    So I guess I will start with a compression test first.

    Remove spark plug from each cylinder
    Pull the fuel pump relay for killing fuel
    Pull the starter relay and use a wire to jump across
    Turn key to ignition
    Push the starter until the PSI is steady... Record 3 times in each cylinder dry
    Record 3 times in each cylinder wet with oil


    Am I missing anything?


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  9. #9
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    Engine to operating temperature.
    Throttle body wide open.
    Wet cylinder with oil only if that cylinder reads lower than the others.

  10. #10
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    Quote Originally Posted by yoyo View Post
    Engine to operating temperature.
    Throttle body wide open.
    Wet cylinder with oil only if that cylinder reads lower than the others.
    Yea I can't get the engine to run that long. So it'll have to be a cold test

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  11. #11
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    Quote Originally Posted by Kid_Storm View Post
    Yea I can't get the engine to run that long. So it'll have to be a cold test

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    OK, you will still get an idea whether things are good or not.
    Probably throw a charger on your battery during testing.

  12. #12
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    Quote Originally Posted by yoyo View Post
    OK, you will still get an idea whether things are good or not.
    Probably throw a charger on your battery during testing.
    Yea im hoping so... I'll see if I can find one with a long enough cord to reach outside lol... I park on the street.

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  13. #13
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    In my experience a super low mileage engine produced 5-10% on a leakdown test. 20% with high mileage isn't uncommon. Anything above 30% just plain wore out! I do these with all plugs removed and have a helper hold the balancer from turning. It will turn once the cylinder is pressurized! I'm sure you know the process of bringing each tested cylinder to TDC on the compression stroke.

    On the compression test anything over 150psi cold is good. I only pull the plug for the cylinder I am testing. I also spin the engine over 5 times. One test dry and one test wet. On a wet test your lucky to see an additional 20 psi.
    Last edited by CUUDA; 01-13-2018 at 01:19 AM.
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  14. #14
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    I thought you was having this towed somewhere for someone to look at?


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  15. #15
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    Quote Originally Posted by us1champ View Post
    I thought you was having this towed somewhere for someone to look at?


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    I did. They checked everything and concluded it must be inside the engine. So the dealer recommended a compression test which I brokefully denied. I'm gonna try this and see if it gets me anywhere

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