Feeler: Electric fan

[TerryBPP]

I was looking through some old post and got the idea to make a electric fan that would replace the belt driven fan on a 911. It would help gain a few hp and maybe work more effieciently. I would like to design it so it would have the same dimensions as the belt driven fan so it could be a simple bolt in and some relay wiring.

I saw that mikez had a dual electric fan on the bastard 356. Any one know of a place already making a single electric fan? Let me know if there is interest.

[Wil Ferch]

I think you'll have a problem....

The mechanically driven fan pushes air against an "installed" system resistance....think of this the same as fluid pressure drop loss in a pipe.

The belt driven fan will ( for all practical purposes) not be affected ( rpm) with or without this air flow resistance. Unless the motor is a "constant speed" motor ( with or without "load")....it may slow down when it encounters air flow resistance within the shroud passages...it would therefore have to be a heck of a motor, which then becomes unwieldy...I would guess.

But I could be wrong.......

Wil

[TerryBPP]

I consider this turbulance factor and figured I would have to go with a heathly motor. If they can do it on a flat 4 I can do it on a six.

[RickM]

This question came up in a recent thread: Cooling fan HP

Quote from MPDevelopment: "Fan output is in liters/sec 3.0-3.2 engine 1500liters/sec = 3178cfm this takes approx 10hp. Have you ever seen a 10hp 12volt 10000rpm motor?"

[Shaun @ Tru6]

Wil, if I understand you correctly, couldn't you then make some type of rheostat that works off the current going to the tach?

Higher RPMs = more fan speed and vice versa.

I have no idea how you would do this practically, but it strikes me that you have a built in measuring/feedback system for how fast the fan should be spinning.

[kach22i]

Originally posted by RickM
This question came up in a recent thread: Cooling fan HP

Quote from MPDevelopment: "Fan output is in liters/sec 3.0-3.2 engine 1500liters/sec = 3178cfm this takes approx 10hp. Have you ever seen a 10hp 12volt 10000rpm motor?"

Yep, this is something we just talked about.

I said: yes, kind of; It powers the Honda Insight hybrid electric car (13 hp electric motor).

http://www.insightman.com/data1/insightout.htm

PS: That was a interesting thread.

[TerryBPP]

Here is mikez 356 with a dual electric fan setup. So it can be done. Maybe Mike can tell us if it ran hot.

[TerryBPP]

356 outlaw...engine and running.

[Mike Bonkalski]

This will get you 3000 cfm.

[mpdevelopment]

It does not matter if you drive the fan with the engine or with an electric motor, it still takes the same amount of power to drive the fan in fact it is less efficient to drive the fan electricaly due to the use of two machines (alternator and electric motor). The wimpy electric fans you are looking at cannot produce the pressure to force the required cooling air volume through the shroud.

[Tim Walsh]

I've got one question.. why?

In a waterpumper, the fan does have to be on all the time since at 60mph the car is going fast enough to drive enough air through the radiator in order to cool the car properly. In a rear engined porsche you don't have that luxury, the fan must be blowing all the time. WHy change the "blowing energy" from mechanical to electrical back to mechanical, when a simple belt will do. Also with the integral alternator, you eliminate the need for a second warning light to let you know the fan isn't blowing. all in all it's an elegant system, why change?

[MichiganMat]

I have friends that run electric fans on 914s, one on each side of the motor. Not sure how well this will work on a 911 but Im interested in hearing more...

[Porsche Doc]

I have been building them for the 914-4 engine for the last 10 years.
I looked into doing on the 911 engine back then too. I couldn't get a small enought to fit between the carbs, that would flow enought air.
The one you have pictured is 12" dia and that won't fit between ths carbs. 10" is max that will fit. Then there is the alternator prob. how to get that to work.

GooD Luck!

[TerryBPP]

Originally posted by mpdevelopment
It does not matter if you drive the fan with the engine or with an electric motor, it still takes the same amount of power to drive the fan in fact it is less efficient to drive the fan electricaly due to the use of two machines (alternator and electric motor). The wimpy electric fans you are looking at cannot produce the pressure to force the required cooling air volume through the shroud.

You are running to systems on the car already. The drag of the fan and the alternator. I would like to see a dyno showing that the loss of hp would be the same. Let me check out some alternators.

The plus side of the electric fan would be that it would run at full speed at all times.

[TerryBPP]

Originally posted by Porsche Doc
I have been building them for the 914-4 engine for the last 10 years.
I looked into doing on the 911 engine back then too. I couldn't get a small enought to fit between the carbs, that would flow enought air.
The one you have pictured is 12" dia and that won't fit between ths carbs. 10" is max that will fit. Then there is the alternator prob. how to get that to work.

GooD Luck!

Mount the alternator like in a V8 car. Use the crank pully for drive.

[TerryBPP]

By the way, sweet 4 banger.

[MichiganMat]

v-dub engines rule

[Porsche Doc]

Thanks Man!
Mount the alternator like in a V8 car. Use the crank pully for drive.

Thats the easy part.
The Fan is the big deal. I couldn't get a 10" one with enought CFM's

Yes, The electiric fan set up WILL give you more HP.
It will also give you better throttle responce.

The alt is not the big drain on the engine. Its the fan that is the biggets drain on the engine. At least that is what I found on my dyno.

[Chuck Moreland]

This is an idea that I have been considering for some time. The advantage has nothing to do with reducing the HP load on the engine.

In fact as MPDEV points out the electric fan will draw more HP given that both alternator and electric motor will convert power at say 85% efficiency. The fan belt is probably 95%+ efficient. The above of course assumes equal air flow and equally efficient fan blades.

The part many people are missing is that the alternator gets harder to turn as the electrical load is increased; this due to a little phenoma called back EMF. If this were not true we could easily use an alternator to produce free energy, ala perpetual motion machine.

The biggest advantage of an electric fan is better temp control. We can select the fan speed based on temp instead of RPM. Imagine running the fan at 10k rpm to get max cooling even while cruising at 65 mph.

Better temp control would allow the motor to produce more hp because we could dial in AFR and timing more precisely.

The big problems are identified above; air flow. The 911 needs copious air flow. Be careful about those aftermarket fan CFM ratings, they are rated in free air. Resistance to air flow created by cooling fins and other obstructions will cut that down considerably.

An electric fan with enough power to do the job will be heavy, large and demanding of the ALT. Maybe so much as to be impractical.

But keep the ideas coming.

[Porsche Doc]

Hey Chuck & mpdevelopment,

I will have to disagree with the statement that it dosen't make more HP.
And my Dyno dose Too!

The fan its self is the largest load.