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Old 06-29-2019, 12:26 PM   #1
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How many GPM from the water pump?

I'm looking at going to an electric water pump on my rallycross boxster. Anyone know how many gallons per minute the factory water pump puts out?
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Old 06-29-2019, 02:05 PM   #2
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I'm looking at going to an electric water pump on my rallycross boxster. Anyone know how many gallons per minute the factory water pump puts out?
Woody, too much flow would cause the engine to overheat..
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Old 06-29-2019, 04:59 PM   #3
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Woody, too much flow would cause the engine to overheat..
That doesn't make any sense. What counts is how many calories per unit of time are dissipated through the radiators. Too little flow is a problem because the radiators will become cool and become inefficient in dissipating heat. High flow has the opposite effect. Warmer radiators that dissipate heat efficiently.
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Old 06-29-2019, 08:12 PM   #4
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Woody, too much flow would cause the engine to overheat..
I'm not looking to flow a lot more than the factory pump. That's why I'm curious about the factory gpm. There are a few reasons I'm considering going electric. First is cost. a factory water pump is close to $300. From a quick search, the top of the line electric water pumps are going for almost half that much. Some electric water pumps I looked at are only $40! Second is I want more control over flow of coolant. I like the ability to keep water flowing even with the engine off. The type of racing I do doesn't give enough time to cool down. Another benefit will be a small gain in overall horsepower because the engine won't be turning a water pump.
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Old 06-29-2019, 08:30 PM   #5
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That doesn't make any sense. What counts is how many calories per unit of time are dissipated through the radiators. Too little flow is a problem because the radiators will become cool and become inefficient in dissipating heat. High flow has the opposite effect. Warmer radiators that dissipate heat efficiently.
It's been a rough week for cooling systems. Both my wife's subaru and my rallycross Subaru had sticking thermostats. Out of cheapness and lazyness, I removed the thermostats from both subarus and they both run cooler without one.
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Old 06-30-2019, 12:11 AM   #6
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Drop a factory PMS electric water pump into the front and call it a day. You can find them pretty cheap and installation doesn’t seem to be too terribly difficult.
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Old 06-30-2019, 04:48 PM   #7
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Quote:
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That doesn't make any sense. What counts is how many calories per unit of time are dissipated through the radiators. Too little flow is a problem because the radiators will become cool and become inefficient in dissipating heat. High flow has the opposite effect. Warmer radiators that dissipate heat efficiently.
Anker, many years ago ( Fiat racing days) FAZA had to put a restrictor on the output hose of the head, as the water was flowing too fast to allow a proper heat exchange from the head to the water.

By slowing the water flow it allowed a proper heat exchange...

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Old 06-30-2019, 05:34 PM   #8
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I knew a guy with a 944 and an electric water pump that he could control from the cockpit and essentially set the water temp wherever he wanted by speeding up or slowing down the pump. But I guess you still have to start with the right approximate flow... I have no idea unfortunately the GPM :-(
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Old 06-30-2019, 06:26 PM   #9
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Woody; I think what will determine the GPM is the size of the coolant pipes to the front of the car. I know you know the diameter of your pipes, but my thought was for 1.5" id pipe size you could flow 35 GPM at 0 psi. Attached is a chart that can give you various pipe diameters.


https://www.hy-techroofdrains.com/water-flow-through-a-pipe/
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Old 07-02-2019, 03:58 AM   #10
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Woody; I think what will determine the GPM is the size of the coolant pipes to the front of the car. I know you know the diameter of your pipes, but my thought was for 1.5" id pipe size you could flow 35 GPM at 0 psi. Attached is a chart that can give you various pipe diameters.


https://www.hy-techroofdrains.com/water-flow-through-a-pipe/
Thanks!
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Old 07-02-2019, 07:24 AM   #11
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I'm looking at going to an electric water pump on my rallycross boxster. Anyone know how many gallons per minute the factory water pump puts out?
This is an interesting question and not as simple as it seems. The stock WP is belt driven continuously variable based on rpm. It flows twice the gpm at 6k rpm as it does at 3k rpm, less head losses. Electric pumps also vary in gpm a lot based on head loss. You need to match the electric pump flow to the OEM pump through the system to get it right.

You could run an experiment. Do some math and figure out the actual pump rpm while the motor is turning at 6k. Then rig a drill to drive the pump, run water from one 5 gal bucket through the pump > through the plumbing and radiators, back to the motor, and into a second 5 gal bucket. Fire up the drill to simulate the engine at 6k and time the process to fill bucket #2. This would reveal the max flow needed from an electric pump.

Hook up your chosen pump and test it to make sure it meets or exceeds your minimum required gpm through the system. Allow your t-stat to regulate engine temp by opening and closing as needed to keep coolant at 180F-220F.

I don't know anyone who has measured this on a Boxster but it would be very useful in a racing application. The drag racing guys have been doing this for years on V8s.
https://www.chevyhardcore.com/tech-stories/fuel-cooling-ignition-tech/tech-feature-what-you-should-know-about-electric-water-pumps/
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Old 07-02-2019, 09:27 AM   #12
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This is an interesting question and not as simple as it seems. The stock WP is belt driven continuously variable based on rpm. It flows twice the gpm at 6k rpm as it does at 3k rpm, less head losses. Electric pumps also vary in gpm a lot based on head loss. You need to match the electric pump flow to the OEM pump through the system to get it right.

You could run an experiment. Do some math and figure out the actual pump rpm while the motor is turning at 6k. Then rig a drill to drive the pump, run water from one 5 gal bucket through the pump > through the plumbing and radiators, back to the motor, and into a second 5 gal bucket. Fire up the drill to simulate the engine at 6k and time the process to fill bucket #2. This would reveal the max flow needed from an electric pump.

Hook up your chosen pump and test it to make sure it meets or exceeds your minimum required gpm through the system. Allow your t-stat to regulate engine temp by opening and closing as needed to keep coolant at 180F-220F.

I don't know anyone who has measured this on a Boxster but it would be very useful in a racing application. The drag racing guys have been doing this for years on V8s.
https://www.chevyhardcore.com/tech-stories/fuel-cooling-ignition-tech/tech-feature-what-you-should-know-about-electric-water-pumps/
Great idea!

Only problem I see is finding a drill that will go to 6k rpm.
A dremel will, but probubly doesnt have the power to spin the WP
Might need to rig up a motor and pullys to get to that rpm
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Old 07-02-2019, 03:43 PM   #13
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Great idea!

Only problem I see is finding a drill that will go to 6k rpm.
A dremel will, but probubly doesnt have the power to spin the WP
Might need to rig up a motor and pullys to get to that rpm
Because it is belt driven and runs on different size pulleys I don't think the OEM WP runs anywhere near 6k rpm. With a little math and knowing the pulley diameters you could calculate the equivalent WP RPM at 6K RPM motor crankshaft speed. A pulley rig could also be used to gear your drill to the necessary speeds.

Without doing any of this you could probably just use a 12VDC external pump designed for V8 engines and get close enough... maybe 20-40gpm. I like this idea a lot. With a 12V WP and a 12V PS pump you would remove a lot of parasitic drag from the motor and get better steering, better cooling, and higher reliability. Probably 15-20 HP at higher RPM.
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Old 07-05-2019, 11:30 AM   #14
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How about an electric water pump with a stand-alone controller that varies pump speed in response to cooling needs ?
https://daviescraig.com/?gclid=EAIaIQobChMIu4SqyMGe4wIVCLbICh0toQcpEAAYASA AEgJk0fD_BwE
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Old 07-07-2019, 04:04 AM   #15
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How about an electric water pump with a stand-alone controller that varies pump speed in response to cooling needs ?
https://daviescraig.com/?gclid=EAIaIQobChMIu4SqyMGe4wIVCLbICh0toQcpEAAYASA AEgJk0fD_BwE
That's pretty much what I was thinking but on a cheaper scale. I like DC water pumps, but I was thinking of using a generic rotary switch. I would control the flow myself by keeping an eye on the temp gauge.
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