Over feeding an impact crusher will actually give the opposite effect of what you are probably trying to achieve. You want greater production right? Then over feeding is not the way to do it. Impact crushers do not run on the choke fed theory. Jaws and cones need to be choke fed as they work on gravity and compression. Where as impact crushers work on actual impact force (inertia) from the rotor blow bars that impacts the rock sends it at speed into the impact aprons. If you are over feeding the chamber you will reduce the rotors ability to throw the rock against the aprons. Along with turning it into a big pepper grinder and eventually stalling out the crusher.