Electric water pump, yes or no?
Discussion
Invading from the S world again 
. As the RV8 a bit longer in the tooth than the V8S I thought I'd try this in the general engine forum. Has anyone tried a electric water pump or got some experiences of one in a RV8 
.
Only asked as it is one of the things being considered at present. A recent RR session where the belt flew off a during a run showed a 10+bhp jump, thinking now is if its not too expensive could be a useful gain to be had.
Harry
. As the RV8 a bit longer in the tooth than the V8S I thought I'd try this in the general engine forum. Has anyone tried a electric water pump or got some experiences of one in a RV8 . Only asked as it is one of the things being considered at present. A recent RR session where the belt flew off a during a run showed a 10+bhp jump, thinking now is if its not too expensive could be a useful gain to be had.
Harry
Remember you'd still need to supply the power from somewhere. If the pump requires 10bhp to run it, then you would have to stick 10bhp through the alternator to power the electric one. You'd need to uprate the alternator as well.
There may be some efficiency gains - ie it's possible that an electric pump of the same pumping ability might use say 8bhp compared to 10 for a belt driven one, but I doubt the gain would be significant.
The same would apply to air conditioning, uses around 5bhp to run off a belt-driven compressor.
I suppose, if you wanted to take a chance, you could switch off the electric water pump for a few seconds if you wanted 10 extra bhp for an overtake. Wouldn't fancy it myself tho'.
There may be some efficiency gains - ie it's possible that an electric pump of the same pumping ability might use say 8bhp compared to 10 for a belt driven one, but I doubt the gain would be significant.
The same would apply to air conditioning, uses around 5bhp to run off a belt-driven compressor.
I suppose, if you wanted to take a chance, you could switch off the electric water pump for a few seconds if you wanted 10 extra bhp for an overtake. Wouldn't fancy it myself tho'.
The electric one will make a big difference to consumed "power" in the form of BHP.
The alternator only tops up the battery in normal use as its the battery thats supplying the moving power for electrical appliances.
Yes youll get some load on the alternator, but i doubt itll be anywhere close to what the fan belt and impeller impose....try it out and see what happens!
The alternator only tops up the battery in normal use as its the battery thats supplying the moving power for electrical appliances.
Yes youll get some load on the alternator, but i doubt itll be anywhere close to what the fan belt and impeller impose....try it out and see what happens!
I suppose one of the other advantages could be that when you sit in traffic at tick over the electric gizzmo could be set to give a higher flow than standard tickover does on the mechanical arangement. Agree in principle about what you are saying about the power required to run it, basic physics I suppose you don't get something for nothing,energy is converted etc.
Still like to hear from anyone that has done it and what the results where
. Harry
deltaf said:
The alternator only tops up the battery in normal use as its the battery thats supplying the moving power for electrical appliances.
Not so.
The battery only supplies current before the engine starts. Once it's started the alternator supplies all the electrical loads and also sticks current into the battery to replace the energy you used starting. If you put an ammeter in the battery lead it will show a few hundred amps flowing out of the battery while the starter motor is running, then as soon as the alternator kicks in it shows current flowing into the battery, and will continue to show current flowing into the battery until you switch the engine off.
I think there is some scope for power saving with an electric water pump. AIUI the water pump is essentially a centrifugal impeller and therefore has a basic characteristic of shifting water at a rate proportional to the square of its speed. It may be that if the pump is sized to provide an adequate flow rate at low revs it ends up being way oversized at high revs and wastes power. An electric pump whose speed is not governed by the engine speed may use about the same amount of power at low revs but less at the top end.
There are also economic/efficiency tradeoffs in the design of the pump. When designing a mechanical water pump for mass production, drive power is "free", so the impeller ends up being a really crudely designed and cast thing to save money. With an electric pump, more drive power translates to more expensive copper in the motor, and more hassle providing cooling for the motor, so it makes sense to use a less crude, more efficient impeller design.
I looked into this in some detail a while ago. As you know my V8S does have an EWP fitted but this assists the mechanical pump rather than replacing it. Without going in to the details, reduced engine temperatures increase power and longevity. The power taken by the mechanical pump is well spent, this is not a good place to try to save power.
I've looked into this a bit and spoken with people who have done this. There are in line plastic pumps from Oz (but you can get them here) which work well and they can be controlled electrically to give high flow at low speeds and lower flow the rest of the time. I think they work from a temperature input. The results seem to be good.
There are also some US race type pumps which can be used on their own and the same company also offers an inline unit to support the stock factory pump.
Lastly there are mezziere electric pumps which replace the whole water pump casting but I don't know if there is a model for the rover/buick. I don't like these. Stevie turbo will probably know who makes what.
I'm going to use the inline electric pump from Oz on the ls1 engine. You insert into the hose and being plastic it hardly weighs anything.
There are also some US race type pumps which can be used on their own and the same company also offers an inline unit to support the stock factory pump.
Lastly there are mezziere electric pumps which replace the whole water pump casting but I don't know if there is a model for the rover/buick. I don't like these. Stevie turbo will probably know who makes what.
I'm going to use the inline electric pump from Oz on the ls1 engine. You insert into the hose and being plastic it hardly weighs anything.
deltaf said:
The electric one will make a big difference to consumed "power" in the form of BHP.
The alternator only tops up the battery in normal use as its the battery thats supplying the moving power for electrical appliances.
Yes youll get some load on the alternator, but i doubt itll be anywhere close to what the fan belt and impeller impose....try it out and see what happens!
If the pump takes 10bhp to power it, that 10bhp has to come from somewhere. If you can get more energy out of an electric motor than you've supplied it with in the first place you've just invented the solution to all our energy problems.
And this time next year, you'll be a millionaire.
greenv8s said:
If those are the Davies Craig ones, the biggest pump they do still only pumps a fraction of what the mechanical pump puts out. Maybe you're talking about another brand though.
It could be them but I'm not sure. The US firm are these people:
www.stewartcomponents.com/html/products/electricwaterpumps.asp
Now, if we could combine their pumps with a temp sensor and variable flow we'd be rocking
I haven't looked into the pressure flow characteristics but those looks a lot more substantial than the ickle Davies Craig pumps. I still have reservations about reducing water flow at peak revs and throttle, and this (reduction) seems to be the only reason you might want to replace the mechanical pump with an electrical one.
Andrew Noakes said:
The electric one will make a big difference to consumed "power" in the form of BHP.
The alternator only tops up the battery in normal use as its the battery thats supplying the moving power for electrical appliances.
Yes youll get some load on the alternator, but i doubt itll be anywhere close to what the fan belt and impeller impose....try it out and see what happens!
If the pump takes 10bhp to power it, that 10bhp has to come from somewhere. If you can get more energy out of an electric motor than you've supplied it with in the first place you've just invented the solution to all our energy problems.
And this time next year, you'll be a millionaire.
Sarcasm? Hmmm i do a great sarcasm myself...but anyway.
The 10 hp isnt only being lost in driving the pump, its also friction from the extra drive belts and their tension.
Bear in mind also that most car water pumps are only circulators and not pressure pumps, basically assisting the convection currents that occur inside the water jacket.
Want to gain the 10hp for free? Run the pump from a spare battery like a DMC red top or similar and recharge it before you go out, ie, its not connected to the charging circuit....or you could have a battery monitor thatd disconnect it from circuit when full throttle was applied and runs it from the auxiliary battery...? no? solar cells on the roof then!!
Can i have that million now please?
You could certainly run the electric pump from a separate battery, in fact you can even buy a gadget that isolates the alternator completely when you floor the throttle so all the electrics run off the main battery.
However you power it, the water pump requires a substantial amount of power. It isn't just helping the water gently circulate under convection, its pumping a high fow rate against a significant back pressure. This is why the pump takes several bhp to drive it. An electric pump of equivalent capacity would consume several KiloWatts of electrical power, for a 12v system this means it needs hundreds of Amps. It just isn't sensible, and if you look at the pump specs you will see that they actually have a much lower rating than the mechnical pumps. In terms of efficiency there is a world of difference between driving an alternator through a drive belt, losing 50% of the power within the alternator and a further 50% in the motor (and another 50% in the battery if you use a battery cutoff) versus simply connecting the belt straight to the water pump. But I don't think the efficiency is the important thing here. If you want as much power as possible, compromising the cooling system, and allowing the engine to heat up generally and develop hot spots in the heads is absolutely the worst way to go about it. Its well known that engines can run more efficiently when they are hotter and can produce more power when they run colder. Wind up the cooling system, lower the engine temperature and increase the water flow, these changes allow you to run higher compression and more advance without developing hotspots in the heads - hostpots which would encourage detonation and reduce the engine life. This also leaves you with more spare electrical power to drive one of those neat little electric superchargers ...
>> Edited by GreenV8S on Monday 28th June 22:06
However you power it, the water pump requires a substantial amount of power. It isn't just helping the water gently circulate under convection, its pumping a high fow rate against a significant back pressure. This is why the pump takes several bhp to drive it. An electric pump of equivalent capacity would consume several KiloWatts of electrical power, for a 12v system this means it needs hundreds of Amps. It just isn't sensible, and if you look at the pump specs you will see that they actually have a much lower rating than the mechnical pumps. In terms of efficiency there is a world of difference between driving an alternator through a drive belt, losing 50% of the power within the alternator and a further 50% in the motor (and another 50% in the battery if you use a battery cutoff) versus simply connecting the belt straight to the water pump. But I don't think the efficiency is the important thing here. If you want as much power as possible, compromising the cooling system, and allowing the engine to heat up generally and develop hot spots in the heads is absolutely the worst way to go about it. Its well known that engines can run more efficiently when they are hotter and can produce more power when they run colder. Wind up the cooling system, lower the engine temperature and increase the water flow, these changes allow you to run higher compression and more advance without developing hotspots in the heads - hostpots which would encourage detonation and reduce the engine life. This also leaves you with more spare electrical power to drive one of those neat little electric superchargers ...
>> Edited by GreenV8S on Monday 28th June 22:06
But if you pump to fast at higher rpm's you get cavitation. From my own experience with blown rovers and heat soak at idle I always needed more air through the radiator. My cure was a viscous fan ala TR8 mounted on the crank. That cured the heat soak after I had tried everything else. For high speeds I slotted the bonnet and got loads of airflow.
Its not a total non-starter, just don't expect it to replace the mechnical water pump without raising other issues. An EWP is very handy for maintaining water flow at idle where the mechanical pump becomes ineffective, and allows you to keep circulating water through the engine to wash the heat out when you switch off.(Been there done that, does that help?)
>> Edited by GreenV8S on Monday 28th June 23:09
) >> Edited by GreenV8S on Monday 28th June 23:09
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