Peter Dohm wrote:

I don't know of anything that is necessarily specific to any one automotive
brand, but a test procedure from some time in the 1990s has been posted to
this NG a couple of times. As of this time, I can't find it; either because
I can't remember the file name or because it died with an older computer.

There is an article from Contact magazine that has been posted here
before. It states that GM runs at max hp rpm with max load for 265
hours as one test and does the cyclic test I described for 400 hours,
along with the thermal testing you mentioned. However, I have not seen
the actual formal test regime, whereas I have a copy of the 1967 test
regime. In the end, it still doesn;t matter as GM is not to my
knowledge selling reciprocating aircraft engines certified or otherwise
and I have not seen any evidence many of the uncertified engines for
sale are testing their engines at this level.

Charles