The Stovebolt Site Forums The Shop Area Engine Shop Horsepower gain?

Is there a HP gain by running an electric fan vs a mech.-pulley fan off the engine? If so, approx. how much for a 235 ci? Also, where did you get your info?

Here's a quote from another site, thought it might be of interest ...

"The power gain from not using a belt-driven fan is small, by most accounts, the average is in the 1 to 2 hp range, depending on the rpm of the motor when measured. You can calculate the requirement, but you have to know how much air the fan moves in cubic feet per second (horsepower is just a number of watts and so is the work done by a fan).
The biggest plus of an electric is they are SOOOOO quiet and smooth compared to a regular fan. And they only turn when the engine is hot enough to need it. So when the vehicle is up to speed, city driving or highway, if the temp sender says the fan doesn't need to be on, then there is no extra load from either a regular fan or the alternator with an electric fan.

If you have a generator, you will need to upgrade to an alternator due to the amperage needs of the fan."

You will get an increase ONLY when the fan is OFF. IF you were able to replace the mechanical fan with an electric capable of doing exactly the same amount of work, then you would actually lose when the fan is on because you would be converting mechanical (belt) energy to electric to mechanical again and lose in heat dissipated in the alternator, regulator, leads, and fan motor. However, this would mostly happen idling in traffic. Above a certain speed the fan does very little, and the radiator gets most of it's cooling from the induced air from the vehicle moving. At these speeds a mechanically coupled fan (for example, with the fluid clutch siezed) would be a net loss of power. I think that the power you would gain wouldn't be noticable at the pedal though. About the same difference as driving with lights/defrost/wipers on or off.

I don't agree with that. The power loss is because of the hp required to turn the mechanical fan. The alternator is already being turned at all times, so the electrical draw from a electric fan will not put any additional mechanical drain on the engine.

Since removing the mechanical fan lessens the hp drain caused by friction, there will be a net gain.

I run an electric fan with a thermostatic switch simply for packaging reasons on my 261. It works great. I do get a slight idle dip when it kicks in, though. It draws 14 amps, which is not a small amount, but it keeps the truck nice and cool. The Delco 10si alternator puts out enough power to run the fan and lights at idle. It's a good setup, I like it a lot.

Tony M . . . The electric fan takes energy to turn and that energy comes from the alternator which in turn gets its energy from the crank shaft.

The electric fan blades are no doubt more efficient than the metal blades on the front of the water pump. Overall, the effective power available to the rear wheels on an intermittant basis is increased when the fan is run from the battery/alternator - an electric fan requires the same energy at any speed - the mechanical fan requires more energy the faster you spin it. Running the fan on electricity provides a load leveling effect that is not affected by motor speed.

How anal do we want to get? A mech fan with 6 blades and steep blade pitch is gonna suck some HP down. The losses with a mech fan should be quantified thus:
Windage losses, inertial loss, frictional loss in pump bearings and belt(s). And if you're not using a flex or thermostatic fan, the losses increase as RPM increases mostly due to increased windage thru blades.

The electric fan's electrical load doesn't change once the fan is running steady-state. Its RPM and load are independent (mostly) of engine RPM. 14 amps at 14 volts is 196 watts. Since 746 watts equals one horsepower, 196/746 equals .2627 HP, roughly 1/4 HP. Does a mechanical fan draw more or less than 1/4 HP at 3000 engine RPM?

Many years ago, when I went thru 235 in my 54. 1 of my fan blades was cracked. I thought it better to run without fan than take chance of it coming apart at speed. Difference was very slightly noticable but truck would start to creep a bit warmer when sitting still at a stop light. I got another fan and it has been running as it should for years. bottom line is very slight but noticable gain from engine not having to turn fan but not worth it in my opinion.

Not sure about the power gain however I have read somewhere (maybe here?) that putting a new electric fan on an old radiator is a bad idea because they can't handle the increased air flow and it will actually shorten the life of the radiator??? Fact or Fiction?

Do not believe there is a significant difference in power either way, but this is bringing seperating flysh-- from pepper to new levels. Seriously, using an electric fan is only an advantage in convenience and packaging except that they might also bring some negligible increase in efficiency through the use of a thermostat.

Tony, you need to head on up to Folsom and visit the old Folsom Power House. Among other things, they have a deonstration setup wherein you hand-crank a generator and then add load to it. You will discover the generator gets darn hard to turn pretty quick!

It's not just the fact that you are spinning the generator. It resists spinning in proportion to the load on it - more load, more resistance to turning.

So, roughly speaking, it's the same load whether it's a mechancal fan or an electric one.

BUT: those old stovebolts have pretty crude fan blades; whereas most electric ones I've seen have more aerodynamic-looking blades. So it's possible there's a gain from the improved aero efficiency.

OTOH, the electric fan has two energy-conversion (mechanical to electric, electric back to mechanical) inefficiencies working against it.

All it all, it's mice nuts on an old truck. Correct tire pressure makes *way* more difference.

Cheers!
George

I stand corrected. Chiphead is right - I hadn't thought of RPM proportionate windage loss against constant electric load - was thinking to staticly (darn I can't spell) But this should be reduced only to fluid frictional loss with a working clutch fan, no?
Jim.

oops, missed his last sentence, first paragraph... "If you're not using..." Apperently I can't read either.
Jim.