I don't know all the specifics of the FA20 knock control. I assume it's not that different from all the other Subaru stuff--all signs seem to point that way. The Rom Raider links explain how the final timing is calclulated pretty well.
One thing I will add based on my experience with other knock control systems is that inside the ECU is a bunch of signal processing that you don't see. There is a monitoring window in crank angle degrees so that noise from the valve motion is ignored. The signal processor dynamically calculates a background noise level based on another set of learning conditions. So basically, it learns the noise during operation that is not prone to real knock, and figures that into the calculation. It's certainly not perfect and whoever did the knock control at Subaru had to set signal thresholds and sensitivities that would be a compromise to account of production tolerances.
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Originally Posted by mad_sb
Probably not any gains with 98 or 100 on stocke tune as compaired with 93 - 94. Once IAM reaches 1 you won't get any more advance.
With a tune there are certainly gains to be had with 98 or 100, if the tune takes the octane into account.
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He's in Australia. That means he's used to RON, not RON + MON / 2 like in the USA. So his 98 is kind of like USA 93.