[kitcarbp]

Below is a pump flow curve I plotted comparing two different size pulleys for the 429/460 Edelbrock water pump referenced above. One is 5.25" diameter the other is 6.25" diameter. I needed to quantify my coolant flow rates at different engine speeds. Why ? To correctly size the cooling system for its intended use. For reference my crank pulley is 5.75" for both sheeves. For street applications, you want maximum coolant flow where it counts; at low engine speeds with little air flow through the radiator core. My application will be in the 450-480 HP range. The results show by switching from the 6.25" to the 5.25" diameter pulley, you will increase pump flow rate about 19% over the engines speed range. This is a noticeable change. The 5.25" pulley is giving you a water pump speed that is about 9.5% over-driven or in the accepted range for street cars. If anyone knows of an 5.00" off the shelf 2-sheeve pulley, let me know! Remember this chart is for pump coolant flow, not engine or radiator flow since those will be less after you take the head losses from restriction into consideration.

For reference, those of you running electric water pumps (main or booster types) literature on those pumps typically (not all) provide 35-55 GPM dependant only on the voltage supplied. These are more than adequate for low road speed cruising. Higher perf elec pumps can go up into 85 GPM region, while high perf mechanical belt driven pumps (NASCAR as an example) now can exceed 150 gpm pumps for racing applications where rad air flow is intentionally minimized for aero drag reduction reasons, not an issue for street cars.