Late reply!What effect do you think gasoline like av gas would have on it? Is this an E85 thing soley?
It's an alcohol fuel thing, E85 & meth, both are very det/preignition resistant so you can keep banging in timing till the power/tq starts to drop off (ie, tune for max HP/Tq), but when you do that the cylinder pressure rise gets pretty fast & they can lift the heads if they aren't held down pretty firm.
Petrol type fuels will rarely allow enough timing to see the fast pressure rise, so don't make as much TQ & don't lift the heads as readily.
The heads almost always lift around peak TQ rpm.