DANMAS> Whatever horse power is required to drive the fan
DANMAS> from the engine, it will take anywhere from 1.2 to
DANMAS> 2 times that horse power to drive the alternator
DANMAS> to power it from an electric motor. [...]
But the fan is not required at high vehicle speeds so with an electric fan it
shuts off using no horsepower. Some American companies still use a viscous
clutch on large V-8's . This can show dynoed gains of 20-30 HP. See the
Chrysler Engine book. A viscous clutch also has the advantage of being fail
safe. I am not aware of one that would fit the TR range. Sometimes thre is
even a thermostatic clucth fitted which will disengage the fan at low
temeperatures
DANMAS> Now, put that same fan on an electric motor, and
DANMAS> what happens? To move the same amount of air, the
DANMAS> fan will require the same horsepower to spin as it
DANMAS> did before.
>Here's your fallacy. The fan you were using before (on the
>engine) is neither an efficient design (at least on my TR-4)
>nor is is shrouded, so the air it moves doesn't all
>necessarily go where you'd like it to for optimum cooling.
>You can, in fact, break even or a little better by using a
>well designed lightweight electric fan (the old one is
>_heavy_ too) in a good shroud. The real win is that at idle,
>you can move enough air to keep that big lump of iron cool
>even in stop-and-go in New Orleans in summer...
The fans on the early TR's are certainly heavy the fan assembly on the TR4A I
have is a six blade variety with lot's and lot's of pitch. Plus the fan and
the extension weigh about 2-3 pounds. That's a lot of rotating mass.
The most important factor is that the normal fan is only going to draw large
amounts of HP when it is needed least -- at High RPM. At 4000 RPM it may draw
15 HP (perhaps more). That's alot of power power to find in a small motor.
The electric fan will draw power out of the engine when you are sitting in stop
and go traffic or at a traffic light, when you have plenty to spare.
Tom
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