I'm talking about the limits of the detonation resistance of the fuel you're running. You can only push it so far on 93 octane before you reach the limit of the fuel and it starts knocking. In the DSM world, the knock sensor is the primary tuning tool, I feel that you need a wideband to get the fuel curve right but at least going by the knock sensor/timing advance you can avoid going into detonation, even if that method of tuning does lead to running way too rich to mask knock caused by setting the boost too high.