What it does is IT keeps the hot gasses out from your airfilter that sucks it back in the engine .
I can tell you it does not make any diverens in power butt it keeps my engine tidy inside thats the only reason it put it on there.
By the way i moved the breather to the front down where there is cool air because the fumes came in the car .
Its done al for the so cald envirement the old cars din't even have these usely it was just a vent tube that went right back in the carter.