Whoopsy:

If a ECU is not tuned for the higher octane, the car won't make extra power.

Higher octane simply means it's harder to ignite. The 'extra' power simply comes from a higher compression afford by a harder to ignite gasoline. A factory car's ECU has been programmed to ignite at a certain compression pressure, and if that pressure can be reached with a lower octane rating, say 95, then 100 octane is not gonna make more power.

A higher octane gas can only help if the lower octane gas cannot maintain that pre-set pressure, say on a extremely hot day where the intake air is too hot causing the air/gas mixture to reach ignition point before max cylinder pressure.

Exactly what I was saying. Btw: The German Porsche ECU is set to 98 octane, 95 octane fuel would result in a power drop. Not sure about the US ECU mapping (as far as I remember, Porsche uses a different software mapping depending on regions, fuel quality, etc.). However, there is a tiny margin in the software mapping, so it would actually slightly profit from higher octane fuel and especially under the circumstances your mentioned (extreme temperatures, air pressure, etc.). 

Like I said before though, 28 hp or less may not matter much on a 560 hp car.


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RC (Germany) - Rennteam Editor Porsche 991 Turbo S, Cayenne GTS (958), BMW X3 35d (2013)