ztrips

OK, this never made sense to me.. If it requires X HP to turn your mechanical water pump, would it not require the same amount of HP to turn the alternator to produce the electricity to turn the electric pump?

How do you get free HP? I would think that it would actually take MORE power for an electric pump given the inefficiency of the alternator and wiring systems.

Maybe I'l lost, but I'd sure like to know how you create energy out of nothing...

Strick

It's all about efficency.

ztrips

So the impeller design of electric pumps is more efficient than the impeller in a stock pump and that makes the power?

96GS#007

Think of it this way...if you turn on your headlights or cycle your door locks you don't a lose a measureable amount of hp.

If you remove a significant amount of mechanical friction and rotational drag (impeller spinning in coolant) from the engine rotating assembly (i.e. the waterpump being spun by a belt (L98) or off the cam gear (LT1/LT4) ), you incur less hp loss and see that as a gain in hp at the rear wheels.

ASRoff

The main reason the electric is better is because it's a constant speed.
The engine and stock water pump turn a various speeds depending on RPM. At a higher RPM there is more paricidic loss. Thats why the electric pump makes more horespower on the top end of the rpm scale.

The electric pump is turning a constant speed (which is optimal for the impeller design) the stock pump will cavatate at certain RPM just like a boat propeller.

ztrips

Ahh.. Now that makes sense...

CFI-EFI

The difference is in the speed and power to run the pump, at a given speed. The electric pump runs at a constant speed, and therefore has a constant power draw, and load on the engine. As the speed of the mechanical pump goes up, the power to drive it increases (approx) by the square of the speed increase. At 4000 rpms, the mechanical pump takes four times the power to drive as it does at 2000 rpms. And nine times the power at 6000, than at 2000. I agree with your statement of the inefficiency in a power conversion. At equal pump rpms, the electric has to draw more power through the alternator than the mechanical, through the belt. I also agree that the impeller design may play a minor part, because the electric can be designed for one speed. The mechanical pump has to work well at a great variety of speeds.

RACE ON!!!

LT4BUD

Very good explanation......

dock351

Hate to hijack the thread!
But

Anyone got info on this?

On a 1990 L-98, How about serpentine belt issues with using an electric waterpump? Also, if someone deletes the airpump, ive heard its almost impossible to get a belt to fit (thus the eliminator kit). How about if one deletes both the water and air pump--belt fitment issues?
Which electric water pump to get?

65Z01

Also just before you stage up you can cut off the electrical pump, eliminating all drag from it, and turn it on 12sec or so later after you pass the traps.

The trick is how to eliminate the water pump pulley completely without stressing the other belt-driven accessories.

Since this is a rather popular mod on the LT1 I assume it is rather easy there, but wonder about implementation on a L98??

I wonder if anyone has any before/after dyno data on this mod??

Cold_B

I can't see how killing the water pump will help you run any faster. If anything, it would be very detremintal. You would could be introducting alot more detenation. The alternator is going to turn the same amount weither or not the electric water pump is on, so all your doing is using power that otherwise would go to waste, kinda like a turbo. Now if you weren't running a alternator on your track runs, and just had a small battery, then I could see why you would do that, but I would be very very worried about that engine.

CFI-EFI

Same amount??? You mean the same rpms? Sure the speed of the alternator won't change, but the power to drive it is directly proportional to the power output. What you are suggesting borders on "perpetual motion". As in the rest of life, there ain't no free lunches.



Thank you for the complement. I'm happy if I was able to make myself understood.

RACE ON!!!

LT4BUD

[QUOTE=Cold_B] The alternator is going to turn the same amount weither or not the electric water pump is on, so all your doing is using power that otherwise would go to waste, QUOTE]


This is just NOT true.....the power it takes to turn an alternater consists of friction, windage, etc. PLUS the electrical power it is putting out....as in running the water pump..so if your not using anything electrical you are taking less power from the engine...thus better acceleration

Now lets put this in perspective.....water pump takes around 10amps at 12 volt equal 120 watts equals less than 1/6 of a horsepower...BUT as they say every LITTLE bit helps...

BTW I first understand this when a friends father, a mechanical engineer, explained that a car gets better mpg in daytime vs nighttime due to not having to power up the headlights during the day.....true but pretty small difference..

ztrips

[QUOTE=LT4BUD]Of course, the hot spots that would develop in the heads from lack of coolant flow would cause detonation and timing retard. Personally, I'd rather spend a few HP making sure my heads don't turn into three mile island..

TOO_HOTTVETTE

You don't increase drag from the alternator. The alternator is rated for a maximum amount of amps, and a constant voltage. So, it may put out a certain amount of available amps, but it doesn't mean you are using all of them. You add an electric H20 pump and all you do is increase the load on the electrical system, not the engine. If you have a 100 amp alt. and with stock accessories draw a max of 30 amps, you add an H20 pump that draws 20 more amps and you increades your load to 50 amps. The alternator doesn't care because it can give you up tp 100. If you try to overload it, it will overheat (most likely blow a fuse) So, NO drag on the engine. Unlike a mechanically driven water pump, thus the reason you gain a few ponies with the electric water pump......Hey...did they have this debate in the stone age when they went from belt driven cooling fans and the gearheads were putting in electric fans to get some extra HP, and did the auto manufacturers start going to electric fans to....save fuel??? Hmmmmmmmm

TOO_HOTTVETTE

[QUOTE=CFI-EFI]Same amount??? You mean the same rpms? Sure the speed of the alternator won't change, but the power to drive it is directly proportional to the power output. What you are suggesting borders on "perpetual motion". As in the rest of life, there ain't no free lunches.

That is simply not correct. The alternator will make maximum power at a given rpm. It may make slightly less at idle speed. But once it gets to it's max output speed all amperage is available even if it isn't used. The burden of providing required power is on the wiring, NOT the engine. The alternator is a seperate system and MAKES power. The alternator will drag the motor 5hp, for example, and that's it. It wont matter if all your lights are on or off. It will always use those 5hp. The alternator will always have 100 amps available, if you draw only 10, it will (the internal wiring) will be cooler, if you draw 90 amps, the wires will be hotter. That is why you have fuses, so you don't pull more amps than a wire can hold. So, the power aint free because the alternator is using the 5hp constantly.

65Z01

An alternator is simply an AC generator with a full wave bridge and a voltage regulator.

As such it provides pulsed DC into the load, which contains the large capacitor, knows as the battery, that smooths out the pulses into a steady DC power source.

Now the work done (P=I * V) by the alternator at any time depends on the load applied across this power supply system.

To verify that this load is variable simply clamp an current meter around the alternator power lead and a volt meter across the battery terminals, start the engine and turn on various accessories to see if the power varies. Actually you can simply raise engine speed and measure the increase in current draw required by the fuel injectors and dist.

Though the difference in power required to drive the alternator may be insignificant there is a variation with load across the power supply.

jfb

I see a lot of misconceptions about alternators in this thread!! Let me see if I can clear them up. An alternator converts rotational mechanical energy into electrical energy. If no current is being drawn from an alternator, the only torque required to turn it is due to bearing friction, fan losses (there is a fan in alternators to cool them), and friction of the brushes against the slip rings. These losses are very small. When you put a load on an alternator (like headlights), the alternator requires much more torque to keep it turning. Headlights draw about 10 amps (140 watts) and 754 watts = 1 hp so the higher the electrical load on an alternator, the higher hp is required to the alternators shaft. The amp rating of the alternator is the current that it can deliver continuously without damaging the alternator. A 100 amp alternator doesn't generate 100 amps, it generates 14.7 volts and the current that flows out of the alternator is determined by the electrical load resistance on the alternator according to Ohm's law, I = E/R. If R is infinite, the current is zero, if R is 14.7 ohms, 1 amp flows, if R is 0.147 ohms, 100 amps flows. The voltage regulator in the alternator does 2 things, it keeps the output voltage at 14.7 volts and it limits the output current to 100 amps (or whatever current rating the alternator has). It limits the output current by dropping the output voltage to protect the alternator. If you short an alternator (.001 ohms) its output voltage will be 0.1 volts and 100 amps will flow out of it (E = IxR, 100x.001 = 0.1 volts). If you connect an electric water pump to the alternator, the alternator requires more torque to turn its shaft and since alternators are about 90% efficient, if the electric water pump motor draws 0.5 HP, the alternator will draw 0.555 Hp (0.5/.9) from the engine serpentine belt.
An electric water pump turns an impeller just like the mechanical water pump, so there isn't a huge difference in hp requirements between an electric water pump and a mechanical one (at the same rpm). If the thermostat is wide open, then the mechanical water pump draws less hp from the engine when its rpm is below the electric water pump rpm (electric water pump motors run at constant speed) and the mechanical water pump will draw more hp from the engine when its rpm is higher than the electric water pump.
The engine supplies the hp to turn a mechanical water pump and the engine also supplies the hp to turn an electrical water pump because the alternator supplies the current for the electrical water pump.
It would be best at the drag strip to turn off the alternator so it doesn't rob hp from the engine and for the run down the strip, let the battery supply current to the cars electrical system and to the electric water pump for 12 seconds so the engine gets cooling and detonation won't occur. Hope this helps!

LT4BUD

Sorry but this is just not true!!!!!!!

jfb's explanation above is another good one....it is true

Rich & Lisa_84

This is exactly what I learned.