The main purpose of the hot water bypass is to allow the heater to function when the thermostat is closed. A secondary purpose is to allow any trapped air in the cooling system to be purged which is an important attribute on many of the Ford engines when looking at how the coolant must flow up and then back down in order to get coolant back into the block from the water pump. Rather than block the bypass in order to increase the water pump capacity, I recommend simply putting a restrictor in the bypass hose or line so that the air can still be purged. I’ve blocked and/or restricted the bypasses on both SBF and SBC engines in racing applications which helps with overall cooling.