In a message dated 97-08-12 18:49:53 EDT, 105671.471@compuserve.com (David
Massey) writes:
> 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 whether
> the car is idling or at redline. And if you use a thermostatic switch the
> fan is off most of the time anyway.
Dave:
In my original post, I said "for the same cooling." That applies to whatever
RPM the engine is operating at. If it takes 21.6 HP to operate the mechanical
fan at 4800 RPM, it will take at least 26 HP to operate an electric fan with
the same air flow.
I also said, in my second post on this subject, that there are many reasons
to use an electric fan. The arguments you make in your post clarify this, and
I agree with them totally (although I believe your numbers are high - the
mechanical fan would provide about the same air flow at 2400 rpm as the
electrical fan, and would consume about 0.1 HP at that speed. I don't know,
so I won't argue the point).
My original point, however, is still valid. Many people are of the opinion
that it does not take engine power to operate electrical accessories. People
have responded to this thread with just that concept. I remember quite well
in the energy crisis of the '70s, that people were asked to turn on their
lights to remind others to conserve energy. The idea being that electrical
power was free in a car. Not so! The whole point of my original post was to
point this out.
For anyone contemplating a swap to an electric fan, it would be a good idea
to have all the facts. Anyone making the swap to gain 18 HP, especially at
normal driving speeds, will be disappointed. Likewise, at normal driving
speeds there won't be a dramatic increase in economy. Due to the sporting
nature of our cars, they are most often driven around windy, twisty, roads,
at a relatively slow speed. An electric fan would be on quite a bit under
these conditions.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
|