Do you have any references? I've seen this mentioned in the past but have not heard of anyone that's done it. I can't expect that it really hinders that much performance, but any amount should help. Mostly I'd like the ability to keep the water pumping faster at idle then with the belt drive and also maybe use a turbo timer or something similar to keep the water pump running for a minute or two after shutdown. I'm sure that doesn't matter as cars are meant to handle the heat when they stop after a drive, but it always seemed bad to me how quickly the temp rises 20-30F on a hot day after shutdown as the same water lays ontop the head, etc. Some of my vehicles like my motorcycle run the electric radiator fan at anytime, so even without the key in or the electric on, after a ride when the engine that just turned off heats up it'll cool down the radiator. This doesn't make a lot of sense, but running the radiator fan AND the water pump would make a lot of sense.
I'm curious if anyone has figures on exactly how much water a mechanical water pump pump and is there any other considerations to look at other than gph, like pressure differntials or anything? The pressure in the system is created solely by the heat, right?
Ok, just found one site, snipets:
The radiator cap will usually hold 15-18 psi, if the radiator holds the system at 15 psi, the boiling point of plain water will be raised to 250° F. The water pump can then make an additional 40-45 psi in the engine and bring that boiling point close to 300° F. So as you can see, pressure is important.
So the pump does build pressure:
Many aftermarket companies offer electric water pumps. Many of these pumps do not flow well or build sufficient pressure in the block. They are only good for limited drag racing use, and when used they need a high pressure cap to help prevent steam pockets. If you are considering an electric pump, don’t settle for anything that flows less than 35-40 gallons per hour and that may not be enough. Many of these pumps flow less than 20gph and cannot keep up with the demands of street driving.
It does however go on to state that 20gph is more than the mechanical pump puts out at idle, so you'll actually get better cooling at idle and stop and go traffic, it's just if you're road racing or continuously above 4-6krpms that the 20-40gph will be insufficient and you'll really need the mechanical pump, but we as hypermilers would never be in the rpm range. It does sound like there's added worry that the pump builds less pressure and there could be internal steam pockets (because the boiling point would be less than 300F), I'm not sure how much of a worry that is.
It would seem that the stop and go and ability to cool after shutdown would be much more important to a street car but the article says otherwise... so who knows. I would think a 2 or more step pump would be best, one that flow 20-30gph (a 'sufficient' amount) below 3-4krpms and then double that rate above that. Unfortunately I don't think anything like that exists and if it does it'd be very expensive and draw a lot of power.
That's the other consideration, you'll be using the alternator to generate electric for your electric pump, that's two points to lose energy to inefficiency (generating the power and using it to drive an electric motor) vs the mechanical pump.
This works out fine and almost as a savings for the electric radiator fans, you definately feel it in the engine and alternator when they kick on, but that's typically at idle when you don't want/need power anyway. The water pump will need to run all the time.
So maybe a better solution would be somekind of waterpump with a centrifigal clutch to hold it at a certain number of rpms. That is, get a bigger pump that flows better at idle than a stock pump, but will only increase flow a little bit off idle and will still be inefficient for extended above 4-5k rpm use but should increase our efficiency overall. Similar to how the thermally coupled clutch fans were a huge improvement over just bolting a fan to an engine.