Thought I’d start a separate discussion on this, look forward to hearing your comments.
So to review (and most of you know), you get maximum power (force pushing down on the piston) when the combustion completes at a known point after the piston reaches top dead center (TDC). Because the combustion process takes time we have to spark the mixture some number of degrees before (BTDC) while the piston is still traveling up. The number of degrees to advance the spark is largely dependent on RPM because a much faster moving piston means you have less time for this combustion to complete.
Ignite it too early and you get unproductive downward force on the piston while it is still traveling up and knock. Maximum power is obtained by advancing the timing to just below this knock threshold. The timing value of this knock threshold at a given RPM on the S4 engine will vary based on load/boost (how much air and fuel is being combusted), temperature, and of course octane, because a higher fuel octane can cause the combustion to burn in a slower more controlled fashion and complete later, so it allows for more advance. This creates even more power.
Now we get to the timing maps - for a given RPM/load/IAT etc. the tune selects a map value based on an estimated knock threshold for the engine under all those conditions.
If the map is too ‘optimistic’ the knock sensors go off and the timing will retard to below this knock threshold. How many degrees of correction you got simply reflects how far off the map’s guess was. One thing I see people say is “my car pulled timing because of heatsoak”. Technically no - the timing map already knows you’re heatsoaked from your IAT and should have a lower map value for that. If it knock corrected another 8 degrees on top of that, it means it simply means the map was overaggressive for the conditions.
Now the best tuners intentionally put in timing values a little over the known knock threshold for the conditions, so that the tune can adjust to max power. That’s a good thing. I remember on my B5 S4 I had an AMS tune that didn’t knock at all, not 1 degree. Is that a great running car? No it was a slow POS. The map timing values were so low for the conditions it never even touched the knock threshold. I got a GIAC tune and that changed. 8)