I didn't mean to say that it lost power, but that it limits the powerband. Restricting and expanding the flow and travel length of exhaust, you can control the powerband. Racing teams have used this method since way-back-when. My dad's old laydown gokart in garage actually has this, and it is astonishing. You pull the paddle behind the steering wheel once you feel like you are topping out, and you expand the powerband and can go further. I don't really care what that man you linked me to says, I've literally experienced it myself, and it is crazy. Ride an old endurokart if you can find them, they were on most of them back in the day. This would also probably be the easiest way to experience it.