Im NAM-Forum kann man folgendes zum Overboost lesen:
ZitatStandard boost is actually about 10.5 PSI, and overboost is about 15.5 PSI. The way to induce it is not to just slowly put your foot to the floor, but SMASH the pedal to the floor as quickly as possible. It's quite a marked difference in torque between the two boost levels; going from "ok we're moving" to "oh wow it's getting out of its own way now!".
ZitatYou can determine if you want the dyno pull to be in overboost or not. Incidentally peak power will be pretty much the same in overboost or not, just the torque curve is different. Overboost is only enacted below 4500 RPM. In my experience, it stays active as long as you are "totally on it". During my HPDE, the car felt like it was in overboost the entire 20 minute sessions. I think MINI says the overboost lasts for 15 seconds at a time, which means 15 seconds per full-throttle stab. Naturally that'll never happen on the track as you're shifting gears and going through corners.