David Massey wrote:
> >In a message dated 97-08-10 16:54:47 EDT, Jody007@aol.com writes:
>
> >> It's said that you'll gain about 18
> >> horse power by removing the fan.
>
> >That's very interesting. That implies that the alternator is more
> than
> 100%
> >efficient. In other words, it produces more energy that it takes to
> run
> it.
> >Assuming, of course, that you are getting the same cooling with the
> electric
> >fan that you got with the mechanical unit.
>
> >Dan Masters,
> >Alcoa, TN
>
> Dan,
>
> You are forgetting that the engine driven fan is waaaay oversized at
> any
> speed except at idle when it is needed the most. An electric fan runs
> at
> the same speed all the time and consumes the same amount of power
> hether
> the car is idling or at redline. And if you use a thermostatic switch
> the
> fan is off most of the time anyway.
>
> Not so for the fan on the crankshaft. It turns at engine speed. It
> is
> sized to give adequate air flow at idle and the rest of the time it
> pulls
> much more air than is needed.
>
> Consider this: I have a fan (from a VW Rabbit) that draws 10 Amps at
> 12
> volts. That is 120 watts. at 645 watts per horsepower and 50 %
> efficency
> thats about 0.1 HP. If an engine driven fan is sized for the same air
> flow
> at idle then the load on the engine at idle is 0.1 Hp. The power
> required
> to drive a fan is porportional to the Cubed of the speed. which means
> the
> fan that requires 0.1 Hp at at 800 RPM will require:
> 0.1 x 6^^3 HP at 4800 RPM or 0.1 x 216 or 21.6HP!
> At Red line. At normal driving speed (eg: 2400 RPM) it is more like
> 2.7
> HP!
>
> The electric fan draws 10 amps from the alternator. Assuming a 50%
> efficiency the engine load is 2 x 120 watts / 645 = .37 HP! Even if
> the
> fan runs all the time there is a significant net savings!
>
> Dave Massey
> St. Louis, MO
Perhaps I'm showing my ignorance, but doesn't the alternator produce
the same number of amps per rev. So the more revs the more amps with a
max 35 amps for the stock unit? So no matter what the amps being draw,
the hp to drive the alternator remains the same? Or does the force (BHP)
needed to spin the alternator increase with the amps being drawn? If the
first case is true and there are enough amps to drive the Fan, then the
running with a fan would NOT cause a decrease in available BHP from the
engine.
--
Roger Helman 71 TR6 CC67866L
Digimation Inc. http://deepthought.digimation.com/rogerh/
New Orleans La.
www.digimation.com
Voice. 504.468.7898
Fax. 504.468.5494
|