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Thread: normal cyl compression

  1. #1
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    normal cyl compression

    what PSI should we expect on a healthy MM engine? 180? 160? 140? What PSI average have you seen in the real world? Thanks.
    BUCKWHEAT 03 MM 300A-August, '02 mfgr, black w/ blue metallic clearcoat, 94,000 miles, Texid stroker 5.0, #15 Kool-Aide w/ SnakeBite porting, Venom cooling, and upgraded to M122, 3873 of 7839

  2. #2
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    When I did mine, I was in the 180-200 range.

  3. #3
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    What's more important is the variation between the lowest and highest cylinders. Shouldn't vary more than 10%.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
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  4. #4
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    The numbers themselves don’t matter much, different gauges tend to read differently. It’s variation between cylinders you are checking.

    I had 200 in 1-6, 170 in 7, and 90 in 8. That was a problem!

  5. #5
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    Quote Originally Posted by crownvic97 View Post
    The numbers themselves don’t matter much, different gauges tend to read differently. It’s variation between cylinders you are checking.

    I had 200 in 1-6, 170 in 7, and 90 in 8. That was a problem!
    #8 is always a problem unless you've installed a rear cooling mod.
    “When you can’t make them see the light, make them feel the heat.”
    Ronald Regan

    "The only way to deal with the Islamic State - these blood thirsty, blood-drunken, terrorists -
    is to kill them, keep on killing them, until you kill the last one, then you kill his pet goat."

    Lt. Colonel Ralph Peters

    “Be polite, be professional, but have a plan to kill everybody you meet.”
    "I come in peace. I didn't bring artillery. But I'm pleading with you, with tears in my eyes, if you **** with me, I'll kill you all"
    General James Mattis




  6. #6
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    Quote Originally Posted by fastblackmerc View Post
    #8 is always a problem unless you've installed a rear cooling mod.
    Indeed, I have rear cooling mods on the back of both heads now...after getting new heads.

  7. #7
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    Thanks for the comments. My range was tight, 136 average, with 142 high and 132 low. My gauge is a Harbor Freight special....

    Did a leak-down today. Three at 20%, balance under 10%. Smoke test suggests the leakers are exhaust valves. Not critical.
    BUCKWHEAT 03 MM 300A-August, '02 mfgr, black w/ blue metallic clearcoat, 94,000 miles, Texid stroker 5.0, #15 Kool-Aide w/ SnakeBite porting, Venom cooling, and upgraded to M122, 3873 of 7839

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