nothing beats measuring things yourself
like an engineer would
you need to buy a small
"wind speed meter"
and use it to measure
the average speed of the air entering your radiator.
Kestrel makes extremely good ones,
acceptable is the
$31 LaCrosse or the
$20 Eddie Bauer
http://www.amazon.com/La-Crosse-Technolo...osse+wind+speedi have measured myself
with the cheap LaCrosse meter
and also an expensive and calibrated coal mining spec Anenometer
about
3600 cubic feet per minute of airflow
on a 245 HP 360 V8
at idle 570 rpm
with an AC condensor in front of the radiator adding resistance
and the viscous clutch 5 blade fan
unlocked and slipping
so that it was turning about 480 rpm
when the viscous clutch locks
and at higher RPM
the cfm of the air moved
will roughly double with doubled RPM
but the power consumed by the fan
will go up dramatically
... when the RPM doubles to 960
the fan will use between
4 and 8 times more horsepower
( for geeks raise to power of 2.4)
as you can tell from
the wimpy power
of these
13.8 volt DC electric fans,
which you can estimate by multiplying:
volts times amps times 0.8 (efficiency)
then divide by 746
to convert watts to US standard Horsepower
they can not move air in volumes
like a mechanical fan
because their motors dont have the horsepower
somewhere i have a graph of the
power consumption versus RPM
of the viscous clutch fan of a
Chrysler 340 V8,
which also showed the
power consumption of the power steering and alternator.
i have posted that graph on Moparts in the past,
i think it is in the back of John Heywoods IC Engines book.
be aware that the electric fan manufacturers
are tricky in their advertising
.. what they call CFM
is in free air with the fan standing alone,
and is not pulling through the
resistance of the radiator fins or
the air conditioning condensor, or
in some cases additional coolers
on the other hand
the cooling system on factory vehicle setups
are way oversized
... most are set up for
towing trailers
up 6 percent grades in
Death Valley national park in
120+ F outside air temperatures
while staying below
240 degrees F coolant temperature
i have run a
200 mile long
70 mph highway cruise
fuel economy test
with no fan blades at all,
using special NPG coolant
that is only 70% the heat removal capacity
of normal 50/50 ethylene glycol-water coolant,
and observed no over heating
