RJG

Agree. ECU may pull timing and add fuel if necessary if charge air is hot, but doubt if it has sensors in the combustion to notice an increase in octane. Also.....since high octane fuels have additives to slow combustion under higher temps and pressures, high octane fuel has very slightly less energy BTU's. So if engine is tuned for 87, and runs well on 87, best fuel economy is with 87. Higher octane fuels are a waste of money and hurt fuel economy for an engine tuned for 87.