Originally Posted by BuzzLOL
.. Hot Rod mag. said they changed the stock head gasket on their 2002 HT383 to a steel shim and bumped the compression ratio from 9.1 up to 9.6... they didn't mention the thickness of either gasket... they did say 18cc piston dish, .026" in the hole... I also read somewhere's there was a change made to the pistons (& head gaskets?) later... their engine was rated 325HP and 415 lb.-ft., but they got a baseline dyno of 338HP 444 lb.-ft., almost identical to the current ratings of 340HP 435 or 440 lb.-ft. (don't know why torque different at different sources)
There were two design pistons. The second design (and what I think is currently used) is +0.005" bigger.
I don't know if the reason for the bigger diameter piston was because of piston to wall fit or to bring the actual displacement up to 383 from 382.
If the piston is 0.026" down the hole and the CR is 9.1:1, the head gasket would need to be about 0.041". But that puts the quench at 0.067"
Using the same numbers, a 0.015" shim head gasket puts the CR at about 9.6:1- just what HR said they got.
This leads me to believe GM built the HT383 w/a very poor quench distance.