66 replies to this topic

[Lima31]

I was thinking the same thing.

+ Consistent water flow which avoids the high mechanical losses with surging under varying engine speed e.g. drag racing
+ Runs at the efficiency point of an electric motor, and reduces rotational mass, so perhaps 0-5bhp improvement on a dyno
+ More control for temperature management

- Expensive in comparison to mechanical
- Increased size to accommodate motor
- Mechanical pumps rarely break shafts, they usually wear the impellers out first, so they still keep turning - if an electric pump motor dies, the impeller could slow right down or seize, and temperature will climb very quickly

I read the following thread, then decided it wasn't worth the hassle unless I was chasing ETs

http://www.irday.com...80413/8537.html

[Heath]

Drag racing hides so many ills, so it isn't a very fair representation.

I don't know what kind of electric pumps you're referring. I've seen some cars with a small electric motor mounted to drive the water pump pulley alone and I suppose the concept of that seems okay, but that motor has to have a fair bit of grunt to drive the pump hard enough to make adequate outlet pressure, and I don't know what the controlling mechanism of that motor is, what triggers it etc? It makes sense that you would make some power out of not driving it from your crank, because driving a good impeller on a water pump should be a big job. But your energy to drive the motor still has to come from somewhere, so it can't be free power?

The in-line pumps on the other hand are stupid. The coolant circuit that goes through the radiator is one of two or more that need to flow for a motor to work properly. If you're only relying on the low speed circuit through the radiator then your cooling system is doing essentially nothing when the thermostat is closed and the circulation is only varied by the discharge the thermostat wants to let through at the time. If that's all you've got, you'll make less power than you should be making, won't be able to tune it properly, it will use more oil and the life of the engine will be hugely reduced.

There's more to cooling systems than stopping cars from overheating

[Struggler]

Most of the aftermarket units flow water at about the rate of a mechanical pump running at about 1500 RPM. If your only cruising Summernats or drag racing then this may work out for you. If your revving the engine in a burnout comp or similar then it probably won't work out for you.

Also the electric unit cannot pressurize the cooling system like a mechanical pump. This pressure makes for more efficient heat transfer both from the engine to the coolant and from the coolant to the radiator.

JMHO

[Heath]

^ Is there actually evidence that these electric pumps won't cavitate? There are definitely mechanical water pumps that will cavitate and will not cavitate. If they have a pressed tin impeller they are pretty much guaranteed to cavitate their arse off.

Also the electric unit cannot pressurize the cooling system like a mechanical pump.

Yep and if it doesn't get pressurized the boiling point is lower.

Open the floodgates to nucleate boiling.

[S pack]

Also the electric unit cannot pressurize the cooling system like a mechanical pump.

Yep and if it doesn't get pressurized the boiling point is lower.

WTF!

The water pump doesn't need to pressurize anything, all it needs to do is circulate the water with a sufficient flow rate to suit the particular application..
Thermal expansion of the cooling system fluid will take care of the system pressure and the radiator cap will regulate the maximum pressure possible which in turn dictates the boiling point of the cooling system.

The use of anti freeze/ anti boil additives will also affect the boiling point of the cooling system.

[S pack]

Sorry mate, but not if the pressure in the system causes a reverse movement of the water over the pump.....

Cheers.

Sorry DJ you've lost me, please explain!

[Heath]

The water pump doesn't need to pressurize anything, all it needs to do is circulate the water with a sufficient flow rate to suit the particular application..

The more head the fluid at the outlet of the water pump has, the better you can control the dominant flow passages (including your high speed circuits), and the higher the boiling point in the system.

It is one thing to say "I'm not familiar with that idea, please elaborate so I can tell if you're wrong or right; I haven't thought about it enough" and another thing to say "no, you are incorrect" when it's laws of nature that aren't open to interpretation.

No, a cooling system doesn't NEED to pressurise anything, a cooling system doesn't NEED to stop a car from overheating either. A lot of hotted up street cars have chronic problems with cooling systems and people try to solve them by fitting bigger and bigger radiators and thermo-fans and removing the thermostats and shit. But you mention concepts like pressure of coolant in a motor and they dismiss it, like that idiot in my signature who doesn't believe in unsprung mass.

The fact is that rotodynamic pumps do pressurise fluid. You can put a pipe going vertically on the outlet of a water pump and keep on extending that pipe until water doesn't flow out of it, and it will stall. The height at which it won't flow any more is the highest head it will produce, that's physics, and it's relevant.

Edited by Heath, 13 June 2011 - 01:32 AM.