Compression check

Discussion in 'Technical' started by riporter, Nov 16, 2003.

  1. riporter

    riporter Member

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    O.K. guys, I did a compression check today on my engine. The Hi-Lo range on all eight cylinders was 170- 160 psi cranking and 95-90 running.
    Other than these numbers running in the 10% parameters they should be in they really dont tell me anything about the internals of the engine ie; does the engine have a cam, flat top pistons, or what.
    The pressures seem high for a stock engine...maybe a mild cam with flat top pistons?...or medium cam with stock pistons....who knows.
    I know very little about the internals of the engine other than what I was told and not sure how much stock I take in that.
    What do yall think?
    Thx Rick
     
    riporter, Nov 16, 2003
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  2. riporter

    riporter Member

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    To be honest I kinda went around my elbow to scratch my behind on this one. There was a slight hesitation in the engine I couldnt figure out where it was comin from so I worked in reverse order.
    Turns out I found the problem in the vacuum system.
    The vacuum line from the carb to the distributor was pulling so hard it was retarding my timing on takeoff.
    After the fix I shaved more than a second off my 0-60 time which is now at 6.6 seconds.
    I dont know but I dont think a stock 302 can turn that kind of time. This thing SCREAMS out of the box.
    It's still good to know my compression is what it ought to be.:clap: :bananaman
     
    riporter, Nov 17, 2003
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  3. CACollo

    CACollo Member

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    I'm sure i'm wrong (it wouldn't be the first time), but i thought that a larger cam usually gave less pressure because of the excessive overlap? I.E. my old combo gave 140 with flat tops, 58cc chambers, and a 108 lobe separation cam.
     
    CACollo, Nov 17, 2003
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  4. mavman

    mavman Member

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    cacollo, that's right! In general, a larger camshaft will REDUCE compression pressure. Why? because the intake valve closes a lot later than it normally would with a stock camshaft. It's not uncommon for the intake valve to close 30-50 degrees AFTER bottom dead center. Normally, a stocker closes 0-20 ABDC. That's what gives a larger cam its sound...as the piston is moving upward, some of the fresh mixture is pushed back out of the cylinder and into the manifold, causing reversion. Just makes it run a little rough at low speeds. That's not a bad thing though:D
     
    mavman, Nov 17, 2003
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