I had a Super Stock hemi racer friend of mine that could run alum or iron heads on his car and always preferred to run the iron heads because he said they made more power than alum. He was limited to the same compression ratio with either head. On a street motor I believe the rule of thumb is that you can close to a full point higher than iron heads and not have detonation problems because aluminum dissipates heat faster. So my question is this. What if you run an aluminum headed motor with 9.0 CR. What would be the consequences?