Gengis
I believe in the world of cars dynomometers (sp?) can be programed to compensate for variations in the temperature and pressure that the test is carried out under to give an equivalent to one taken under ISA conditions. So you could ask engine manufacturers to do the same (unlikely to be helpful) or you could possibly ask the man from you nearest engine tuning house if he has some tables that would give you the correction factors. Or possibly see if a dyno manufacturer would be prepared to let you have a bit of there software.