<VV> Electric cooling fan vs Belt driven

[John David Thomson]

Being a mech eng by vocation, I just have to add my two cents worth (thats now about 2 cents US up here in Canada!).

You cannot get "Up to 14 free HP!" by converting to an electric fan.  It is just not electrically/mechanically possible.  You might save a small amount of horsepower gain depending on the fan efficiency , but you have to remember that the electric power to run the fan must come from somewhere, and that somewhere is the alternator. As noted by many contributors to this session, electric fans draw quite a lot of current and this comes from the alternator, which then is a HP load to the drive belt from the crank. 

As well there is an inefficiency with an electric fan as you use mechanical energy from the crankshaft to convert to electrical energy then again convert that electrical energy to mechanically drive the electric fan. Each step that changes the form of energy looses some energy due to the conversion equipment losses.  

The primary reason that GM (and the other major producers) chose to go to electric fans on the new vehicles is that water cooled engines can have the fans runs slower when temps are okay.  With the electronic control systems on these newer vehicles (IE 25 to 30 years newer than the Corvairs we own), they can slow the fans down and use less power than a belt driven fan that will always use the same power level (remember the "thermostatically" controlled fans in mid 1970, they used those for the same reason = less power draw).

So for us regular drivers with air cooled engines, stick with what you got from GM.   For the autocrossers, they have the solution of half speed fans (change pulley dia).    

If you want to cool down an autocross car after a run, then the one idea I saw of a portable 12v driven fan that sits right on top of the blower (with some plastic shrouding to cover the blower opening) makes the best sense.
Regards, Dave.........