Quote Originally Posted by Pimp_Daddy_Patty View Post
Unless Mitsubishi is doing something different with their newest ECUs, I haven't come across an ECU that will advance ignition timing beyond what it's originally calibrated to do.

At times of higher ambient temperatures,and prolonged loads that builds higher combustion chamber temps, the ECU will sense knock and apply an amount of knock retard to maintain safe combustion. The result of this is slightly lower power output until the knock threshold returns to it's normal range. In a case such as this, the higher octane fuel would maintain a higher knock threshold which the ECU would not have to pull any ignition timing.

Higher octane fuel typically burns slower, and in an engine only calibrated for lower octane fuel, would actually cause peak cylinder pressure to happen a bit later after top dead center. This in turn can lower power output by a small amount. From my experience in adding turbo kits to NA engines, I would typically advance timing in the vacuum range of the ignition map to maintain part throttle power and fuel consumption. The difference isn't much, but I still managed 40mpg on cars that never attained such fuel economy numbers in factory, NA form.
I co-sign this. Using higher octane is a waste of money in the mirage and it's a placebo thinking it improves performance.

Doing it enough could actually cause carbon build up and its bot able to burn as effectively.