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Whats the compression on a stock 350?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by K5thatShmobs, Oct 3, 2002.

  1. K5thatShmobs

    K5thatShmobs 1/2 ton status

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    When using a traditional compression tester (in the spark plug hole) what would a healthy compression reading be for a stock 350 engine?

    Thanks
     
  2. 95 Silverado

    95 Silverado 1/2 ton status

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    when using the tester, be sure to block the throttle plates open on the carb or tbi so the engine can get air. readings from 80 to 120 lbs. are common, the thing to watch for is "are all the readings close to being the same", watch for any cylinders that seem lower than the rest. that can be a better indication than the actual pressure reading.
     
  3. imiceman44

    imiceman44 1 ton status

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    You will need a rebuild soon if you have between 80 and 120 PSI.
    What you want to see is more like 160 to 190
    190-200 is almost new or newly rebuilt with good results, that's what I have on mine.
    150-160 is what you would expect from an engine that's seen some action but was maintained well and still can go for a while.
    As was mentioned, the most important is difference between cylinders.
    You should have no more than 10% difference between the lowest reading and the highest reading.
    You would be better off with 120 accross than 190 in one and 150 in another and the rest 160.
    Get the picture?
    There are ways to check if you have different numbers to see if its worn rings or bad valves or valve seats.
    Skirt some oil in the cylider and try again, if you get better numbers you have bad rings, if you get the same, you need to look at your valves.
    Need more...
    IceMan
     
  4. ntaj*ep

    ntaj*ep 1/2 ton status

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    Mostly YA, what he said! /forums/images/graemlins/grin.gif
     
  5. Waxer

    Waxer 1/2 ton status Author

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    he said "stock" 350 engine, and the number for that would be 150psi.
     
  6. Z3PR

    Z3PR Banned

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    Doesn't it also depend on year of the motor ??? Late 60's / early 70's engines had higher compression then late 70's through late 80's, in the 90's compression started coming back up I do belive.
     
  7. Waxer

    Waxer 1/2 ton status Author

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    Yeah you might be right. I have a 74 and the compression for that is 150. I posted all my numbers a LONG time ago here asking for an analysis. Since then I have bought a crate motor.
     

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