The pressure the crank gets has to do with the ratio used to release the disc. I do not think it is possible to have a good enough release ratio to allow a 4000 lb clamp load to release. RPS also moved the pivot point of the casting to allow better release ratio many years ago on the Z plates. Again when you make enough HP to need a 4000 lb clamp load you would want to use at least a twin disc. A twin disc doubles the torque capacity using the same clamp load. A twin disc is a much better solution and would also provide less wear due to more friction area.