Is there no sprag clutches avaliable that would disengage themselfs after say 4250 rpm etc? As a lot of aircraft components such as air driven starter motors are constantly driven after they have started the main engine, but over thier start speed the centrifugal clutch disengages and allows the drive to freewheel .



Or how about an electronic viscous drive? the angle of the plates are controlled to vary the drive, so you could have full drive at low RPM, and a quick but progressive tail off over the revs you want? Sure they use this in active diffs etc, and again they are used on aircraft (called CSDU's, constant speed drive units) to drive items that require a constant speed, such as engine driven generators, hydrulic pumps etc