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only it's not that the combustion is more intense (hotter) with higher octane, it actually releases less energy than the cheap stuff, but only a tiny amount. the benefit of higher octane fuel comes from it being harder to ignite. There are two components to ignition which are temperature and pressure. water boils at 100 C at sea level, but at a higher than atmospheric pressure it would boil at a different temperature (which is why you use different rad caps to keep your coolant from boiling). Similarly the intake charge (air and fuel) will ignite at different temp when you increase the pressure (more boost or compression). There are many factors that will determine when the charge will autoignite like AFR, cylinder pressure, temp, and the type of fuel, but generally speaking the higher octane fuels will allow for harsher conditions in the other categories without autoigniting before the spark event as compared to a lower octane fuel. And harsher conditions in those other categories all add up to more power.
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