[LightningGSX]

Power is greatest when peak chamber pressures are just after TDC, when chamber volume is at its least.And higher the octane = slower the flame speed and greater delay in peak chamber pressure.So for greatest power, your octane is limited by the amount of ignition advance available or visa versa.Or for every amount of octane there is a certain amount of ignition advance needed for best power or vise versa.So after a certain point ,increasing either alone results in no power gains.And since you(or your ecu) can only advance your timing so much, there is a fine line when octane is actually bad.I personally think even c16 is too much for the average modded 4G63(no proof speculation only), but since you can't start at 100 octane and work your way up point by point I guess you have to go with what you can get.