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456M GT

Discussion in 'Technical Q&A' started by George, Apr 3, 2005.

  1. George

    George Rookie

    Nov 2, 2003
    11
    I am contemplating the purchase of a 99 456M GT with 24000 miles. I am told the compression readings range between 210 and 245 (two cylinders are at 219). These are differences of ~16.66 % and ~11.8%. Is this a safe buy? Are these readings acceptable?
     
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  3. Mike-456M

    Mike-456M Rookie

    Jun 10, 2016
    22
    The variation is a bit wide, but certainly acceptable. I do question the actual numbers, however. The 456M has a compression ratio of 10.6:1. Given the fair amount of valve overlap in these engines, readings above 200 psi seem abnormally high. The readings on my 456M are in the 175-190 psi range. I suspect the gauge you used is out of calibration, or the cam timing is incorrect.


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