Why do FLOWKOOLER hi flow water pumps cool BETTER THAN OEM?

Whether it is in stop and go traffic, a slow moving parade, in line at a car show, off road on the trails or hauling a heavy load up a grade all cars face reduced airflow through the radiator at slower speeds.  FlowKooler hi flow water pumps push twice the coolant through the system at these lower speeds and help the engine transfer the heat.  The result is engine temperature reductions of up to thirty degrees, increase system pressure in the engine block which reduces ping and improved flow efficiency which means more horsepower. 

Doesn't the coolant have to have more time in the radiator to cool?

In a closed loop heating system if you keep the fluid in the heat echanger your also keeping it in the block longer. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. You have a far better chance of keeping your cool with a greater flow rate through your heat exchanger than gathering heat in your engine block.