Is the electrical fan conversion any good?

[NoHachi]

jondee86 Wrote:Now, the Fan Laws say that the power absorbed by a fan varies as the
cube of the rpm. So, even in the absence of any data on airflow or
pressure, I have no difficulty in believing that the OEM fan could absorb
8 hp. Dyno testing is probably more demanding than actual road use,
as there will be less airflow thru the radiator from the external cooling
fans. And the viscous coupling tightens up as it gets hotter.

I've been taking a look at fan related websites..for example:
http://www.engineeringtoolbox.com/fans-e...d_197.html

If I punch in some numbers, say 1500CFM =~2000m2/h at any pressure rise (usually negligable in cars) I come up with an "ideal "power consumption of between 0.04 and 1.00 kWatt.. more or less in line with what I expected..

You have to punch in some crazy numbers to explain an 8hp drain. For example:
- that the fan has to work against a pressure difference of more then 2Bar (usually in a car, the pressure tends to work in your advantage..the little fan certainly isn't able to bring underhood pressures to anything remotely positive...wish it could though..cheap boost!)
- the fan is pushing more then 10.000m3/h..or around 6000CFM! (for reference..big block V8 dragster fans..designed for short and heavy loads in circle track and dragracing push around 3000CFM.)
- some very poor efficiency numbers..only possible if toyota got the design completely wrong..

Would love to see some some fan-law calculations to see in which ballpark they end up.. My feeling is that its between 0 and 1 hp (@crank).

Look at it from another perspective..an electric fan replacing the OEM fan would have to pull similar numbers.. lets say its about 50% more efficient (huge!) then it would be close to a 4kW current draw.. any idea how long the combination of alternator and battery would sustain that? (stock alternator =~ 1kW).