I had problem with this too, till i ffigured out what the "cutout" does.
Boost cut out is a little lever that prevents the throttle from going all the way forward (in the "red")
If you disable cutoff,you will be able to move throttle a little bit extra.
But if you already have your throttle at 100% you won´t be able to push it further so you have to move it back a bit to "reset". and then you can get that extra 10% (or whatever). You will hear sound effects warning you that its not a good idea to leave it for long
But the cutoff itself does nothing to your power. Look closely at the throttle and you will figure it out.