Hmmm - good to keep in mind, maybe one day when I get desperate for horsepower I can have this one up my sleeve, the alternator trick is interesting as well.

As for electric water pumps,if it's a daily...don't go there as you may end up having cooling problems in traffic snarls,constant ideling etc.as the coolant is getting wizzed through the radiator that fast that the coolant gets no chance in the core to be cooled by the fan pushing air past.

Now for competition where your running between 5000-9000 rpm constantly they work a treat and also reduce cavitation which you get around 7000 rpm with a standard pump.
Even with an electric pump for racing you still require some sort of flow resistor(modified thermostat) to keep water in the cores a bit longer to be effecient.
And yes,you will pick up a couple of free HP with an electric pump.

Nice discussion guys I understand now too!

I pulled out the Bosch Handbook checked out alternators - indeed the more current required, the greater the magnetic field, the greater the torque required to turn the alternator shaft.

Thus turn on headlights - more torque required to turn alt - rpm may drop.

Best thing is I was right and my mate was wrong....I better make a phone call.

Thanks again - this is what forums are all about.

ok cool understand.

yes dodgeman, i meant to add "mechanical"

Peper is right in this regard, the 'mechanical' resistance to rotation doesn't change [brush drag & bearing resistance] but the electromagnetic drag, well that's different & this is seen at the pulley in the same way that it would see mechanical resitance.
It's just 'load'

The alternator is a form of electromagnet: As the alternator spins, the magnetic fields cut through each other to produce a voltage/current output.
Higher electrical load requirements by the vehicle mean stronger internal magnetic fields, which equates to greater rotational resistance (the alternator is harder to turn, so robs more hp from the engine).

A friend has developed a system where he can open circuit his alternator via a dashboard mounted switch. It gives him extra hp for hillclimbs etc (dyno proven), but can only run for a short time (otherwise it kills the battery). This is dependent on your ignition system though - his is aftermarket (distributorless with coilpack) so doesn't seem to suffer when voltage drops from 14v to 12v.

Quote:
this `is where people are getting confused.
the alternator never ever gets harder to turn, the ENGINE has to work harder to turn it so it can supply the needs of the car.

Quote:
the resistance to turn the alternator doesent change. your confused with what people are saying.

Elecricity is created by passing a conductor through a magnetic field [or vice versa] That's oversimplifying it but it's also true.
In an alternator, the magnetic field is provided by the rotating element inside the unit & the strength of this magnetic fiels is varied by the amount of current passing through its windings. This clearly means that it is an electro magnet & the regulator 'regulates' just how much power is fed into these windings.

In it's simplest form, the lower the electrical load, the lower the strength of the electromagnetic field, but as the electrical demand rises, so too does the strength of the electromagnetic field [controlled by the regulator] & as a consequence the electrical output of the alternator also rises.

The mechanical load that the engine sees is provided by the magnetic field inside the alternator. The engine must pull the [electro]magnets away from the stationary iron poles of the stator within the alternator during the normal rotational operation & if you have ever tried to separate two strong magnets, you will get some idea of what's happening in there in a continious cycle.
The more electrical power output that's needed, the stronger the magnetic field, the greater the mechanical load.
No free lunch.

Electric water pumps not recomended for street use? Not hard to see why.
My comments refered to volume of coolant that is pumped but made no reference to 'over pressurising' whatsoever, so I don't know where that came from.

hmm I doint know, u r suggesting that the alternator increases its resistance as more electrical load in accessories is drawn?
How does it do this, from what I can tell the internal brushes are at a light pressure to the magneto etc and that doesnt change.

dodgeman what u r saying about electric water pumps over supplying and over pressurizing the system before thermostat at idle is true, the question gets asked in Street Machine or Hot 4's write in sections often and they always recommend
its not a good idea for cars built mainly for street use.