Aluminum heads with a low compression 440 will loose compression? Huh?

The premise in post #5 is what I have kept hearing about, so the theory is that the alum head needs about a one point higher CR to have the same power as a CI head. I do not buy it, never have, but also have no proof one way or the other....
What I DO know is this: the mixture burn is completed in a few milliseconds. I do not see how there is enough TIME for heat loss...