Too many Chrises (pun);
All of those production Chev engines have their service limitations.
In the last 20 years the "heavy" castings have gone and have been replaced with lightened engine components.
There are special considerations when mounting aluminum heads on a light weight block.
The different rates of thermal expansion has to be taken into account when choosing gasket material, sealant, torque rates, head bolt design, and so on.
The entire package is nomally quite reliable until more power is attempted to be extracted from the stock design.
Aluminum heads on cast blocks may be more sensitive to engine overheating or operation in a place like "Winterpeg" with -40 winterpeg temperatures, than iron production engines.
(whats that song from Neil Young?)
Take into consideration the design MAX hp GM lists in the block section of their performance catalogue, before adding NOS and a turbo.
(the NOS is there just to get the turbo spinnin')
The owner can have an influence (pun) on the reliability of his or her performance engine by not modifing or removing the engine's temperature control devices such as the *&^%$#* thermostate.
Also it would be advisable to not work the engine until it is up to temperature, and not shut down the engine when it is very hot.
[ September 03, 2003, 03:38 AM: Message edited by: userfriendly ]