New heads?

AJ/FormS said
Ok, say I believe you.......
So
how come I can run near 200psi on 87E10 with no detonation?
Whereas with iron, the limit is down around 160/165
Both at WOT/optimum timing, and otherwise identical

You tested identical heads? Both in exact design and combustion chamber shape, except one was aluminum and the other iron? What were those heads?