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Thread: Normal Compression on a correctly timed 1996 N*

  1. #1
    IXSLR8 is offline Cadillac Owners Member
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    Normal Compression on a correctly timed 1996 N*

    Does anyone have an idea on what normal compression is for a correctly timed 96-99 Northstar engine when tested with a compression gauge?

    General Engine Specs: Heads were done at a shop. The shop said they were beautiful before they did any fine tuning on them. I strapped them down with studs, inserts and Cometic gaskets. Engine has approximately 50K on it.

    Context: I'm currently working on a N* in another vehicle and am trying to determine if my compression indicates that I'm out of time by a tooth on my intermediate shaft to crank chain. I keep getting a PO300 code stating random misfiring and I've replaced all engine sensors, wires, coil packs, plugs, etc...:

    Compression test (Cranked Over for 5 seconds):

    1-145 lbs.
    2-150 lbs.
    3-150 lbs.
    4-150 lbs.
    5-150 lbs.
    6-150 lbs.
    7-150 lbs.
    8-170 lbs.


    Second Test (while running):

    1--75 lbs.
    2--80 lbs.
    3--83 lbs.
    4--80 lbs.
    5--80 lbs.
    6--83 lbs.
    7--85 lbs.
    8--83 lbs.

    Any thoughts are appreciated. Thank you, Dave.


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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Normal Compression on a correctly timed 1996 N*

    The 150 psi group is perfect. The 170 is high (carbon ???)

    I have never done a running compression test and see no need for one.

    The guideline is that all cylinders should be within 10% of the mean - you're still in the ballpark.

    Are the coils/plugs connected exactly as shown in the diagrams ? That's critical to prevent a nagging miss.

    Click on the diagrams to enlarge.

  4. #3
    IXSLR8 is offline Cadillac Owners Member
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    Re: Normal Compression on a correctly timed 1996 N*

    Thanks Sub. for your help.

    I thought the compression looked pretty normal except for the high number 8 cylinder. I was thinking carbon too.

    I'm very sure that I timed the motor, as per the posted diagrams, when I did the block inserts and such. I was hoping to see if my compression readings, as compared to someone elses correctly timed northstar, would tell me anything about my timing. This is the first time I have done a running compression test. Someone mentioned to do that kind of reading as well.

    I was thinking that I may be off a single tooth on my counter balance shaft to crank sprocket but have the cam chains correct. I have a mild misfire and get the P0300 code as mentioned. I've replaced just about everything I can think of and am now second guessing the timing work I did.

    Once again, thank you sir.
    Last edited by IXSLR8; 03-08-10 at 04:28 AM.

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Normal Compression on a correctly timed 1996 N*

    Hmmmmm.........Call Jake up in Canada at Northstar Performance - www.northstarperformance.com

    or go back and find some posts by MikeLawson - he does some Northstar work out near Lexington, KY.

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Normal Compression on a correctly timed 1996 N*

    If I recall correctly it is pretty easy to get the Northstar timing off by a tooth. I remember our old Guru mentioning something about rotating the crank 7 times to get it back in sync or something like that.


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