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Thread: Need some advice after compression check

  1. #1
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    Need some advice after compression check

    My donor is a 2004 WRX with 164K miles. It had a new short block installed at 60k. Compression test shows all cylinders at 125psi. cold. It also has about 15lbs vacuum when warm. I don't intend on racing the car, but may have some limited track time. I want to keep the cost down and do not intend on putting more than a few thousand miles per year on the car. So I want reliability and basically stock motor, or warmed slightly if cost effective. I am thinking basically rings, bearings, timing belt, water pump, oil pump, valve job.

  2. #2
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    Wayne Presley's Avatar
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    That's low on compression. I'd do a new Subaru shortblock and have the heads done.
    Wayne Presley www.verycoolparts.com
    Xterminator 705 RWHP supercharged 4.6 DOHC with twin turbos

  3. #3
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    If the heads were not done with the last short block replacement I would almost assume thats the cause of the lower compression. Otherwise you would think a short block with 100k miles wouldn't be that bad already

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    Thanks Wayne, your comments are much appreciated.

  5. #5
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    Thanks for your feedback. I will know more when I get it apart, hopefully, just some headwork.

  6. #6
    Senior Member SixStar's Avatar
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    Compression tests should be done on a warm/hot engine. Cold numbers are not a useful measure.

    Get engine to temp, fans on, fans off.
    All plugs out.
    WOT.
    Crank 10-15 times.
    Owner/builder - AEM Intakes 818R #85

  7. #7
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    the numbers being grouped together is more important than the numbers themselves. on a cold engine i'd say those numbers are fine. keep in mind these are low compression engines and the final numbers have a lot of variables at play, like engine temp, condition of compression tool, crank time etc.

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