Hello. I have a 86.5 5 speed. I am thinking of replacing my belt driven fan with an electric fan. There are a couple of kits out there. One is a single fan, with a temp sensor that is spliced into the radiator hose. The other is a twin fan setup, amd I believe replaces the stock temp sensor. Has anyone used these kits? Thanks, Kip.

 

I replaced my belt driven one with a single electric that I wired a switch in that is located under the front fender. I turn it on after it warms up and let it run a couple minutes after i shut it off. Just fuse it where it grabs its power. I have seen double lectric set-ups too.

Just have to balance the draw against the air it pulls. Mine does a good job. You need to keep the cowl around it.

 

Contact Dave Lomas@ Motorsport.
His drop in plug & play twin fan set up is super trick.
Will set you back about 600 pancakes but will net you 13-15 more ponies.

RDS

 

This does look cool, but dont expect anything NEAR 15 hp gain (or saved) more like less than 1hp. If you dyno'ed more, then the savings is due to something else.

you show me a driven fan on our cars that blows the heck out of the air, and ill show you the same fan driven by 1/2hp motor that spins just as fast.
also, the fact that i can cool my engine down below the middle heat line with my stock S4 fans, tells you that 13amp each, or 26amps total is 338watts. remember, thats electrical power! divide that by two, and you are looking at less than 1/4hp mechanical. say the belt driven fan is way better...... well, still only about 1/2hp .

ive taken the S4 fans, separated the fans and only use the single off the temp switch (old late modle style). I also have them separated by two relays, and a manual on switch for the second fan if temps get too high. usually , by the last few laps of the race, ill turn on the second fan. in otherwords, the S4 fans can actually keep my engine cool in ALL conditions and for street driving, the single on one side of the radiator, does the job. (again, each fan is 13amps or so)

Mk

 

Dave has dynoed a car after removal of hydraulic clutch fan and air pump and significant gains were noted.

RDS

 

ive measured the force to drive both. Less than 1 hp for both. pretty simple stuff here. any gains found were not due to the removal of the fan. reason, it doesnt take more than .25hp to drive the driven fan on our older 928s.

have you seen an air condioner fan? its coicedentialy the same diameter as our 928 driven fans. they put out a lot more air flow at 3000rpm with a .25hp motor, again remeber, thats electical current in, not mechanical out. divide by 2 again, and thats 1/8 hp output. to spin our fans as fast as they can be spun, is less than .25hp.

If i gave you all the benifits of doubt, it could be 1hp. Even if i took that same AC fan and DOUBLED the speed, that would require 8x the hp. so, 1/8hp x 8 is 1hp. thats Still not 15hp and its not remotely possible to spin our fans at 6000rpm!

ever spin a air pump? it spins freely . very little friction and power required.

so, you have the fan, and two belts with friction, and the air pump. if it gained 2hp you would be incredibly lucky. think about a 2hp lawn motor engine! there is a lot of power to drive the things we are talking about!

Again, most of the gains dave saw, were not due to the fans and ac pump.

If you dont believe me, talk to someone else that deals in these kind of motorized mechanisms on a day to day basis.

I removed mine for the 1-2hp and the weight, as well as less mechanical things going on to break, and less stuff to mess with when doing a timing belt or water pump!

quick formula for fans. 13 ( power x diameter x eff) ^2/3 = thrust in lbs. (ie mass flow) This means that diameter and power are the main factors and thrust is due to nothing else. pitch, style, etc are all efficiency factors.

The friction force will effect hp required directly proportional to speed. there might be 2-3ft-lb of force to rotate the preloaded belts on the fan and the air pump. at 6000rpm the hp required to spin them, without the fan forces is 3x6000/5250. or near 3hp. also remember, at half the speed, there will only be 1/2 the hp required. if you look at Dave's dyno run curves, you would see the original curve and the "stuff removed " curve as two lines that are really close together at the start and then greatly diverge at the 6000rpm . if they are kind of evenly spaced, as i suspect that they are, that would prove the gains are not due to aerodynamic forces nor frictional forces.



MK

 

Were the electric fans turned on during the dyno run?

 

I went with the 928 Motorsports fan Kit. It fits in side the stock fan shroud, so no cutting or mods to that is needed. If you don't like the temp switch you can get a relay kit from spal and wire it off the ignition. See this thread-->Fans and shroud thread

 

Thanks for the responses guys. I didnt mean to start a horse power debate. I am looking for a more effecient way to cool the engine. A replacement clutch fan is about $340 and the single electric fan replacement is about $220. If I get a gain in hp that would be ok, but I am more interested in cooling. Thanks, Kip.