All showerheads are restricted to the same maximum flow. The only thing that is not regulated is how many shower heads you can put in the stall. If the head has a removable restrictor, then you can increase the flow by removing it. Flow volume is determined by both pressure and flow capacity. With a given shower head, and without a compensating flow regulator, if the pressure is increased flow will increase, and if the opening size in increased, flow will also increase, but pressure will decrease.