I disagree.
Fact: It takes "X" amount of energy to move "Y" CFMs.
Fact: A *Fixed* fan has NO HP loss moving "Y" CFMs of air.
Fact: An electric fan has energy loss in
many places: Mechanical to Magnetic energy in the alternator; loss in the AC to DC conversion ; loss of the voltage regulation; loss of the inefficient fan motor, and so on.
I think I said it nicely on the corral.. I'll try to summarize:
o Dynos for fan changes are
BS!
o For city back to back driving where you never go over ~10-20mph, a *good thermal* clutch fan is best.
o The Stang came with a
good OEM thermal clutch fan.
Not some POS speed-only clutch or some POS thermal clutch.
o For a fan of
equal CFM ability to the
good OEM thermalclutch fan, you'll see maybe ~5HP gain above ~3K-4K rpms. Back in the 90's there were a few "real" dynos done on the OEM thermal clutch fan vs an "equal" electric fan.
o A PWM controlled electric fan is the best. Next is the 2-speed. The single speed fans are horribly inefficient at idle compared to a *good thermal clutch* fan.
o At highway speeds, electric fans rule! No HP loss. A thermal clutch fan will take ~3->7 HP depending on rpm.
o In most cases, doing a dyno with a fan is a [/b]joke[/b]! It has very little to do with the
real world! Especially on a car with a very tight engine bay like the stang! At ~55mph, about ?70%? of the HP that the car used is used to overcome air resistance. Now, in a
tight engine bay, there is a LOT of air resistance between the fan and the engine. Opening up the hood, blowing AC cooled air into the radiator, and so on has
nothing to do with the
real world!
o For the track, you want a fan that you can shut off just before the run and that you can keep on just before the run. That way, you have the coolest engine possible with no HP loss at the run. The
decrease in engine temp alone for an electric fan is worth it for a track car. The electric fan will cool at lot even at idle. But, the clutch fans don't.
Like I said, there are
many many factors that going converting between mechanical energy and electrical energy in real life. At work, I have to worry about even *very* small percentages.
So, in general, a 2-speed fan is pretty good. A PWM based control for an electric fan is the best since it can control the *required* amount of air flow the most accurate (thermal clutches are okay, but not very accurate).
For bumper to bumper city driving, go with a thermal clutch. It'll last a long time, you can have a more aggressive pitch on the blades, and there's no battery draw.
I said my piece. Yea, many other will disagree. That's fine. I know what I do for a living and I know what it's like having to deal with real world conversion of energy.
Opps, want to add.
For a Stang, that has poor engine bay air flow and restricted outside air openings, you want an electric fan because it can move it's max amount of air flow even at idle. The thermal clutch fan is limited by the engine speed. So, for cars that tend to overheat, even though a thermal clutch fan may move more CFM at 3K+ engine rpm, for cars that get hot
at idle, you want something like an MKVIII fan. At idle, the MKVII fan will kick the clutch fan's *ss in moving air. But, it'll also take more HP. Sorry, you can *not* get "energy for free". Once again, for a big fan like the MKVII, you want either a PWM controller or a 2 speed controller. In general, you shouldn't need the full fan speed at idle.
JFWY
