octane levels

Just seems to be common knowledge. Not only compression ratio factors into it. Things like piston design, head chamber design, ignition timing, outside conditions, like you mentioned aluminum heads.

Seems to be '10:1' is 'max' for 91/93 octane with cast iron heads. And 11:1 is 'max' for aluminum heads for their tendancy to remove heat faster from the combustion chamber. Excessive heat = can lead to detonation. Octane is rated in 'antiknock' resistance. Charles law, higher pressure = higher temperature. Lower pressure = lower temperature. The more pressure you put into that cylinder (compression ratio), the more heat, and the more 'antiknock' (octane) you need to safely run it without detonating.


Atleast thats my understanding of it at the moment. :D