[b3lha]

Originally Posted by oab_au

...we would have to change the spark advance, with different octanes.

Isn't that exactly what the ECU does?

It was my understanding, from reading the Subaru ECU patent that the ECU has a base timing map for the lowest octane fuel it can burn, and a maximum allowed advance map. The learning system starts off with the base timing and then gradually advances it until it detects knock and then backs it off a bit.

Since discovering that the JDM cars have different fuel and timing maps to the UK and USA cars, I've been running mine on 99 octane. I think it runs smoother on 99. If I can't get 99 and have to use 95 or 97 instead, it runs rough for a while.