They do not reduce detonation but you can run more compression without detonation issues. WTF do I have to do, write a AJ long thread with all the disclaimers?
You can run the same compression with both. WTF, I’ve typed that out a hundred times...head materiel does NOT affect what fuel you can run or what compression ratio you can use.
The coolant can’t absorb the spike in heat fast enough to make a difference. Like I said, the EM test only showed what happens when you heat load an engine way beyond what it should be. That’s why we have transmissions...downshift on a long pull and don’t lug the engine.
