ORIGINAL: JB71RT
Do the HEMI's use aluminum heads? If so they can run a higher compression ratio because combustion chamber temps are lower compared to an engine with cast iron heads. This helps with detonation. Even better if the block is aluminum too.
Yes, they have aluminum heads, pretty much every engine has that these days. In fact, cast iron is becoming rare for engine blocks these days. The only problem is aluminum heads are not quiet as durable and abusable as cast iron so there is a degree of trade off.