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Compression, leak down test results interpretation

Discussion in '206/246' started by HMB-Dino, Aug 12, 2010.

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  1. HMB-Dino

    HMB-Dino Formula 3
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    Jun 28, 2010
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    RonG
    #1 HMB-Dino, Aug 12, 2010
    Last edited: Aug 12, 2010
    A Euro Dino I'm looking to buy went through its PPI and I have the compression and leak down test results, but I'm not sure how to interpret them. The car has been driven very little over the last year or so but the engine was rebuilt ~10k miles ago.

    The PPI inspector seems to believe the results are good given how little the car has been driven and suggests the variation in compression results should `even out' with more use and valve clearance adjustments.

    The results are as follows;
    #1 186 psi/5% leak down
    #2 192 psi/3% leak down
    #3 188 psi/3% leak down
    #4 176 psi/4% leak down
    #5 172 psi/4% leak down
    #6 185 psi/5% leak down

    So is there agreement that the results are good under the circumstances?

    How about the PPI inspector's assessment on what would improve them?

    Are there what would be considered `ideal' results?
     
  2. BigTex

    BigTex Seven Time F1 World Champ
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    Bubba
    #2 BigTex, Aug 12, 2010
    Well, you want compression to be in a tight 'range" so that doesn't look bad, and others know more about the leak down but that looks okay too.

    He's right engines "sitting around" can stiffen up the rings and running and frequent oil changes free the up improving things.

    Let's see what experts say....
     
  3. dignini

    dignini Formula 3

    Aug 21, 2005
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    Luigi Marazzi
    #3 dignini, Aug 12, 2010
    No expert by any any any means,
    but figures only mean so much anyway.
    5% leak down and 10% compression differential could be OK to some. Could also indicate the thing is not even run in yet
    Now run the car for five or six hundred miles, up and down the rev range, vary the load, make it work a little. then test again. Otherwise you will be talking about theories for a long time!
    If you need to buy before you do that, then it will be more of a seat in the pants decision.
    Do you like the rest of the car?
     
  4. Ferraripilot

    Ferraripilot F1 World Champ
    Owner Project Master

    May 10, 2006
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    John!
    #4 Ferraripilot, Aug 12, 2010
    Those are great leakdown numbers IMO. My brand spanking new engine leaks down around 2% or less on most cylinders.
     
  5. HMB-Dino

    HMB-Dino Formula 3
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    RonG
    #5 HMB-Dino, Aug 12, 2010
    In general, I like it a lot. Paint redone in last 2 years (down to bare metal), upholstery redone recently, PPI indicated rock solid suspension, engine solid up to red line, only 46k miles on car. It has some warts that hopefully won't be expensive to resolve, some over time. But I'm identifying select issues that I'll need quotes on to decide if they'll affect pre-PPI agreed selling price. And not being familiar with Ferrari's and buying `classic' cars at all, I want to make sure the engine isn't a yellow or red flag.
     
  6. michael bayer

    michael bayer Formula 3

    Aug 4, 2004
    1,293
    #6 michael bayer, Aug 13, 2010
    I agree w said above, an engine that has sat for years compression numbers are often unreliable as they are likely to get better with miles. Many a good engine was needlessly rebuilt because the new owner didn't get it back to life and run and wait for 500 miles at good speeds to ascertain its true condition M
     

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