# Original engine compression specs GTO vs Grand Prix



## gtoguy389 (Jun 3, 2012)

Please bare with me as I am just trying to learn the subtle differences. I just bought a 1969 Grand Prix over the weekend. It all checks out and is completely original. My research shows that this XH block is equipped with the same 62 heads that came on automatic GTO'S. So why is compression rated at 10.5 on the Grand Prix vs the 10.75 on the GTO? Was the difference in the head gasket? Thank you for helping me learn new things.


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## Pinion head (Jan 3, 2015)

No difference, all in the verbage when the advertised specs were put out for publishing. Have parted dozens of '69 & 70 GP's, had several XH coded 400's from both years. the only between the XH & YS, other than the stamped 2 letter ID code on the face of the block, is the lower horse GP's took a center dump log manifold on the drivers side, the lower horse A body's took a rear outlet log manifold. Actual static compression ratio should be right below 10.0-1 with either engine w std bore block & never resurfaced heads.


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