I have never been able to establish a difference in performance, maybe it's thoery is to provide a smoother power deliver therefore making the bike less draining to ride which ultimately results at the finnish line.
It is baisicaly a primitive type of power valve, that is why it was fased out when the power valve engines were introduced...
Either way its a neat bit of gear going on a very neat YZ465, I'm Happy, Ted's Happy and the horse is Happy!!!!!!!!!!!!!!!!!!!