Electric water pump and power saving?

Road-race engines and ancillaries - general discussion
Mats
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Re: Electric water pump and power saving?

Post by Mats »

Feedback: I went with the electrical unit...

Engine is not up and running yet but I will try to post more details when it happens, if someone is interested.
/Mats Strandberg
turbofiat
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Re:

Post by turbofiat »

Guy Croft wrote:So totally unreliable running an electric water pump, forget about it.

If you want more power build it into the engine, this is a race engine website after all. That's what we do here.

GC
Sorry to dig up this old thread but I was going through some of my posts and found it.

My question wasn't regarding mechanical versus electric water pumps which seemed to be the focus of my post. I should have left that example out. Sorry.

My question was how much drag (power loss) does a mechanical water pump and a 65 amp alternator create on an engine? Is it worth the hassle of disengaging the waterpump through an electro-magnetic clutch and power to the voltage regulator to reduce engine drag just when the turbo is wound up? As I mentioned, this wouldn't be practical on a race car but on a street car I could see how it might be of some benefit.

Here is a good example:

After adding air conditiong to my Spider last summer I could definetly tell when the compressor is engaged. So much so wired in a pressure switch so when the turbo hits 1# of boost, it kills power going to the A/C clutch. I read that a typical "modern" automotive air conditioner compressor pulls around 7 HP.

Non aspirated engines typically use a vacuum switch to kill the compressor under wide open throttle or near it.

I just noted that it seemed like my Spider felt as if it had picked up some additional HP when the V-belt came off. I wasn't sure if it was my imagination or there was something to it.

Thanks.
124 Spider, Yugo,131
pastaroni34
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Re: Electric water pump and power saving?

Post by pastaroni34 »

I have no doubt you could feel the difference without the belt.

Alternator HP Draw:
There are a few things going on here: 1. charging draw, 2. draw to spin the alternator guts (no charging)

1. Charging draw: At its very basis, it takes shaft power for the alternator to generate electricity. At full draw, you could potentially pull 65a x 14.5v = 1.27hp. That assumes the alternator operates at 100% efficiency. In reality, an alternator's efficiency is about 50% depending on many factors, mainly rpm and operating temperature, so lets just say from charging you're pulling 2.52hp. **To do this, remember, you have to pull a full 65a, most of the time though, you're probably not consuming that much power.

2. Spinning the alternator: the interesting thing about the charging draw is that it is always quoted in a steady state. In a race situation, nothing is in a steady state. The engine is constantly accelerating up and down the rpm range. Just like a flywheel, the alternator takes horsepower to accelerate. An OE Fiat alternator is run about 2 x crank speed, so say that in 2 seconds you accelerate from 3500 to 7500rpm, you have to spin up the alternator 8000rpm. With some assumptions on the alternator's moment of inertia, we can calculate this to take 4.13hp. This is assuming the belt transmits power at 100% efficiently.

Another note on alternators, most are rated at a certain %duty cycle. They will perform with a higher instantaneous output than what they are rated at, so while a 95a alternator will put out 120a for say, 30 seconds, as heat builds their efficiency drops and they will reach a more steady state output around their rated output, in this example, 95a.

Water Pump HP Draw:
A subject I don't as much about, it seems very complicated as you have varying pressures depending on open or closed thermostat, pumping efficiency at various rpm, etc. My guess would be about 1hp to pump and negligible to spin up because of its very low MOI. Of course the advantage of an electric pump is it operates at a constant rpm, where it is most efficient, with the added plus of cooling or warming the engine while the engine is not running.

Another interesting point, a 9.5mm (3/8") V belt has a limited power handling ability, roughly 5.5hp. It is not uncommon to exceed the belt's capacity, this means slip, heat, degraded belt performance, and eventually failure. This is why you won't see an alternator rated over about 110a without a double-v or serpentine (poly-v) belt on an OE application.
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA
Guy Croft
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Re: Electric water pump and power saving?

Post by Guy Croft »

I'm afraid all this power-loss technology is beyond me.

Without in any way wishing to diminish (or belittle) the material proffered so far I shall simply remark that if you think the ancillaries are taking too much power you need a more powerful engine.

GC
turbofiat
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Re: Electric water pump and power saving?

Post by turbofiat »

Guy Croft wrote:I'm afraid all this power-loss technology is beyond me.

Without in any way wishing to diminish (or belittle) the material proffered so far I shall simply remark that if you think the ancillaries are taking too much power you need a more powerful engine.

GC
I was just thinking along the same lines as reducing weight. Free horsepower.

Allot of people like to remove the bumpers from 75+ Spiders because the think it's free HP despite it ruins the looks of the car and is illegal in most states.

I weighed both bumpers on my Spider and the they were around 65 lbs/30kg. I gues the same reason my Yugo feels more powerful than my Spider despite making 30 to 40 less HP simply because the difference in weight (800 lbs/360 kg)..

I guess that's why race cars don't have air conditioning. Just something else to create drag on an engine.
124 Spider, Yugo,131
nabihelosta
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Re: Electric water pump and power saving?

Post by nabihelosta »

Ok
I know what I will tell is totally out of subject here, and not applicable, but just some thoughts out of personal experience.
We prepare a BMW E30 M3 (1988) for local hill-climb events, and middle-east hill-climb championship, Group SM class 4. (Super Modified - 2001cc to 3000cc NA engine - minimum 980Kgs curb weight).
The powerplant is borrowed to the newer E36 M3, 3.0 24V straight-six individual throttle bodies, and heavily, really heavily modified. Delivering 286bhp@7400 on stock, it was worked to give 392bhp@9600 dynoed. Everything, from peak performance bottom end, to modified head, valves, omission of VANOS system, 324deg camshafts, dry sump, MOTEC engine management.. is present here to make it a high-revving, and RELIABLE engine.
Our hill-climb races, are held on a stretch of 3.5kms, on uphill twisty roads. Very demanding on engines and transmissions, and more on suspension and LSDs.
As for every NA engine preparator, we are in continuous search and development, trying to "catch" each and every last horsepower available.
Our last mod was this: Switching from mechanical water pump to electric one, and from mechanically driven power steering pump to an electric one too. As both draw too much current, thus more load on the alternator, and more drag on the engine's torque, the horsepower gain was neglictible (less than 2bhp). So we had a somewhat funny idea, but it really worked, although we had too much doubts about it: We moved the alternator from the engine bay, all the way to the cabin, behind the driver's seat, made a hole on the car's floor panel, a pulley on the driveshaft, a muti-v belt, and an automatic belt tensionner.
The engine now has no belts at all. Nothing to be belt driven. The car did succesfully 3 hill-climbs till now, won them all, won the Middle-East hill-climb championship for 2011 for 2WD vehicles. No problems at all of battery draining, especially we are using a compact lightweight 200Ah battery. More important than that, several dynotests showed horsepower going from 392 to 405bhp. Very critical and useful when you are already at your peak power, peak lighweight, and someone "gifts" you 13bhp for practically free :-)
Thank you for reading this, sorry if it was off subject and wasted your time.

Nabih
HORSEPOWERunlimited
Guy Croft
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Re: Electric water pump and power saving?

Post by Guy Croft »

Excellent informative post Nabih, well done.

G
nabihelosta
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Re: Electric water pump and power saving?

Post by nabihelosta »

The post will be illustrated with photos later, soon after the holidays, as the car sits at the bodyshop for now, 50 miles away.

Plus I'm too busy to visit the bodyshop, I'm working on two supercharged M3 E46 powerplants right now, that have to be delivered to costumers before Christmas.

Rear wheel arches and front fenders being reworked, to accept respectively 305/40 R18 and 265/45 R18 Dunlop full slick tyres.

I will also post some photos of the engine, opened and internals showing, when I start disassembling for the annual regular check-up.

Thank you.
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WhizzMan
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Re: Electric water pump and power saving?

Post by WhizzMan »

I know of an Alfa 75 3.2 24V conversion racer that does the same trick. The only things run from the crank are the drive shaft and the water pump (that's still mechanical) and the cam belt. The generator is on the transaxle gear box in the rear. It puts weight lower on the car, in this case, closer to the battery and more towards the centre of gravity. Even if you gain no weight or power, you still gain a lower center of gravity and less inertia turning the car. As you said, you don't do this to every car, since it's a lot of work and the gain is very small, relatively speaking. For the racers that have close battles for trophies, it's well worth trying out.
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pastaroni34
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Re: Electric water pump and power saving?

Post by pastaroni34 »

Nabih,
From where are you getting your dyno numbers? If reading hp at the wheels, and then converting to power at the flywheel, they may be artificially inflated.

I am not trying to discredit your numbers, just trying to reconcile them with some of my calculations.

Thank you
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA
nabihelosta
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Re: Electric water pump and power saving?

Post by nabihelosta »

Jason:
The Motec engine management system we use, can calculate FW horsepower, using data provided from the crank sensor versus wheel speed sensor. Its accuracy is estimated to +/-0.5%, bench-dyno proven several times.

Yes we are aware of the inflation occuring on the wheel dynos, especially when u start changing your gears and final drive ratios, and by huge amounts.
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Guy Croft
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Re: Electric water pump and power saving?

Post by Guy Croft »

I've never worked on a E36 M3 3.0L 24V myself but have heard they can be made to be extremely powerful.

Saw an M3 head last year and flowtested it, no idea what year but not ancient - no way could it be improved and that was as-supplied by M3 - whoever they are!


G
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Re: Electric water pump and power saving?

Post by WhizzMan »

"BMW M" is the division of BMW that does the "M series" of their production line. They also do the M5 and a couple of other cars, the "M power" suspension kits and a whole lot of other sporty accessories. They are also know as BMW Motorwerke and BMW M-Technik. Basically, it's just BMW themselves that have a separate division that get to build the top sporty model for each normal car they build. That explains why there is so much top of the line technology in the M cars, they have the resources, information and funding of the mother company to start each project with.
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TomLouwrier
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Re: Electric water pump and power saving?

Post by TomLouwrier »

hi guys,

As far as I know (google and wikipedia may be your friends here) M stands for Motorsport division. They were set up in the 70's as the official BMW works development group for their racing activities. Over time BMW started to sell (homologation?) specials under the M label.
Mind you: there is quite a difference between a full M-model and a standard car 'with M-options'.

Engines and suspension are very brilliant, very BMW.

regards
Tom
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Guy Croft
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Re: Electric water pump and power saving?

Post by Guy Croft »

Thank you for the explanation of what the M series is guys!

GC
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