924Board.org

[Martijnus]

I agree with daniel... the only way you can control a mechanical fan is the way BMW does it...with some sort of 'visco' fan. But since a waterpump has to be driven all the time (not really true..). I can also imagine that an electric waterpump does indeed take more hp. On the other hand...have you ever felt how much power it takes to spin the stock pump by hand? Imagine that with 6000 rpm. That's a lot of power imho! (but the mentioned 5hp is also quite a lot... )

I'm converting to an electric waterpump too... that's why this thread got my interest. The reason I'm doing it (for street/daily use!!) is to reverse flow. It just can't be done with the stock pump...
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[!tom]

[ideola]

Tom, that's an excellent crash course, thanks for helping me get my head around this.

But as you noted, the motivation (for me) is primarily to precisely control the pump using the ECU, and more importantly, to provide reverse flow through the head for improved cooling.

As for the HP gains, I suspect where I got off the rails on this was looking at the typical drag racing applications, the idea being, you operate the pump while at idle, but turn it off while doing your quarter mile run to avoid the parasitic loss that would otherwise occur if you had a belt driven pump. So the HP gain (or rather, avoidance of parasitic HP loss) is only during very specific circumstances, not 100% of the time.
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erstwhile owner of just about every 924 variant ever made

[daniel]

Hi All
The examples I used are purley arbitrary, for specifics do you own research ect. Also I do not wish to discourage electric water pump use, if you read my thread I have used one myself! Only saying that you wont see HP gains with one installed in a car that relies on an alternator for replenishing of charge.

It all comes down to energy can not be created or destroyed, only converted from one form to the other. But as we all know, if you convert energy from one form to the other (eg mechanical to electric and back again) you incur losses as no machine is 100% efficent.
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[Rocco R16V]

Another benefit of the electric water pump is the motor can change revs quicker. The mechanical water pump has to speed up/slow down the water with every rev change. This additional resistance is eliminated with the electric pump. The alt was there before, the battery smoothes the current load, and the electric’s pump speed can be dictated by heat rejection needs, not rpm.
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"Government exists to protect us from each other. Where government has gone beyond its limits is in deciding to protect us from ourselves. "
Ronald Reagan

[924OZY]

I think its pretty clear that the electric motors used to power these pumps are not big enough to be 5hp, or anywhere near that.
I'm sure if someone has a look,
they will be able to say exactly how many hp it is even capable of draining.
Could also be worked out by the amps and volts required/ or used.
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924 N/A snailshell, superpro linkage bushes, 2.5"exhaust

4.0L ef Fairmont, 3000rpm stall, shift-kit, J3 chip, 3" exhaust, self tuned using tunerpro, soon to be boosted,
expecting 350Kw at wheels at 10psi.

[Martijnus]

[Rocco R16V]