antnicuk

thats a good point, i cant hear it squeal but i cant here much after about 3000 rpm.

I get lots of black dusct buy the belts which is why i pressumed it was slipping.

How can i test the alternator?

antnicuk

So it appears there are very different opinions about weather an E fan is better for power than the stock fan.

My reasons for changing (see above) are not for power so i will give it a try.

Just out of interest:

If you are at WOT on a track doing 70+ mph, is the fan doing anything or does the air going through the rad caused by the speed of the car superseed anything the fan would suck through?

In other words if you never stopped, would you need a fan?

RotaMan99

I think this would be false. The clutch is always slipping. Its never fully engaged. So if the engagment is at say 40%, and you are at 3000rpm, the fan will be at 1200rpm. If you are at 6000rpm, the fan will be at 2400 rpm. The numbers will increase or decrease depending on how much the clutch is engaged. So if the engagment happend to be 80% at 3000rpm, the fan would be at 2400 and so on.

RotaMan99

The fan would not be doing anything. The amount of airflow flowing through the radiator would cool the clutch below its engagment point so it would initially just be free wheeling as best as it can at 25% engagment.

If you never stopped and you were going fast enough for the airflow through the radiator to keep up with the amount of HP the engine is producing which will produce more heat, then you would never need a fan.

clokker

iTrader: (2)

Probably not.
Watercooled roadrace bikes do not have fans...one reason that they hate sitting on the grid before the start of the race. One straggler from the warmup lap can cause all the stationary bikes to begin peeing on themselves as they overflow.

SirCygnus

iTrader: (1)

unless teh stock fan clucth or fan is broken to complete ****, then and only then would i think about getting an e fan. more electronic bs to break imho.

antnicuk

I am off to the Nurburg Ring again in June so need to make the car as releiable as possible, i cant wait for it to break first

NZConvertible

No, and that wasn't what I said, but it is one of the major advantages. Consider the fact that electric fans have been around for many, many decades, but they weren't used on cars until someone decided to turn the engine sideways and needed to use an electric fan on the front-mounted radiator.

Actually we do a lot of work with variable speed fan systems, but I get what you're saying. Engine speed varies widely, quickly and often.

The pulley and belt don't change when converting to an e-fan, so they shouldn't be part of the comparison. And while it's true then engine has to accelerate the fan and clutch, how much they get accelerated depends entirely on how much cooling is currently required. If the radiator cooling demand at the time is low, clutch engagement will be low and the fan speed will not increase much when the engine speed increases rapidly. Worst case scenario is accelerating from low speed after sitting for long enough to increase fan engagement. But you could argue that under the same circumstances the e-fan would also be running and the alternator will be putting increased load on the engine.

Your lightened flywheel analogy is technically correct, but the stock fan is much lighter than a flywheel and most of its mass (the clutch) is concentrated in the middle, so it has far less rotational inertia. That means there's a lot less advantage inertia-wise from removing it. Most of the load it puts on the engine is work done moving air.

Ditto for thermoclutch fan. When it's not required you effectively get a reduction in rotating mass, since it's not being rotated as fast as it could be.

All this technical talk still doesn't prove any significant advantage from an e-fan. Nobody seems to want to perform some very simple before-and-after acceleration testing. All you need is an empty stretch of road and a hand-held stopwatch (not a dyno). Hell, I'm tempted to start looking for an e-fan so I can do this myself.

That's one of the smartest suggestions I've heard in an e-fan thread. Maybe I'll do that too.

I know this. It was a simplistic explanation so people would understand the concpet... Suffice to say that beyond a certain engine speed the fan stops accelerating with the engine. All thermoclutches do this to prevent unnecessary load on the engine and possibly causing fan failure from overspeeding.

RotaMan99

Understandable. It was the way you worded it. I believe that there is a certain point to which the fan will stop accelerating with the engine but I wouldn't say it happends at 3000 rpm, or do you know for sure that it happends at 3000 rpm. I would think it would have something to do with the amount of drag on the fan its self to induce even more slip at a certain point correct?

That is a neat idea. I wouldn't know how to do it though.

Well, this talk shows the possible advantages from the e-fan and also from the clutch fan. As we like to say, converting to an e-fan is more of a side-step and not an upgrade since we realize there wont be a large noticable difference.

jackhild59

iTrader: (7)

This is perhaps the most civil and rational discussion on the e-fan/thermo-fan that I have seen in this forum.

BTW, in the interest of full disclosure: I have an S5 N/A Vert with nearly stock cooling system (evans NPG+ coolant) with factory A/C. It works perfectly in the very harsh heat and humidity of Dallas Texas for the last two summers. I also have an 88 TII project with a Taurus e-fan. I am using it merely for improved access during the restoration. I have all the stock cooling system parts. I will most likely return to stock when everything is finished...

I also have a Gtech pro so maybe someday when I am out of projects I can do some testing on the S5. No promises.

MaczPayne

iTrader: (5)

If you hear your fan go faster as your engine increases in RPM, then your thermoclutch needs to be checked/replaced. The fan should freewheel after a certain rate of speed.

RotaMan99

We try to keep it that way. Its no good when it goes off the deep end. I also agree though.

RotaMan99

Kinda lost me here. Can you explain what you mean by dynamic system? With variable speed fans, you would figure out the HP lose just the same as a single speed fan correct? You just need to know what amount of current the fan is using at a given time....

CyberPitz

The only ONLY reason I'd get an E-fan is so I can reach my damned OMP easier....

is that bad of me?

PS keep up the discussion..we should put this in the archive afterwards haha.

jackhild59

iTrader: (7)

Understood. It is impractical to drive a thermo-fan with a modern front drive transversly mounted engine. Audi was one of the few front-drive longitudinally mounted powertrains in the market. They had packaging issues as well. I haven't owned an Audi in many years, but don't they use thermo-fans? Mine did (1976 100LS). Does anyone know if they still do?

Bingo!

Agreed. This would be valid in a discussion of pure theory comparing the two systems, but in our discussion comparing an RX7 conversion you are correct. I had already lost the ability to edit when I realized I had misspoken/typed this.

I agree. You are an engineer, I am not. I do however have a great deal of application design seminar and field training in air-movement, primarily with axial flow systems.

Question, NZ: Isn't the vast majority of the work done (thus air moved) toward the tips of the fan blade? Thus, the vast majority of the aerodynamic loading of the fan blade is on the outer portion of the fan? And as S.P increases, air will actually tend to flow in reverse through the center of the fan?

Thus one additional advantage of our large diameter fan clutch/hub assembly is to impede the backward flow of air through the center of the fan system? And the curved tip of the blade is to increase the efficiency and work done by the part of the blade that does most of the work?

That being said I also speculate that the aerodynamic loading near the tips behaves very much like an edge weighted rotating mass?

If so, there is one huge difference: Wouldn't the power required to accelerate rotating mass increase at a linear rate while the power required to accelerate the fan blade aerodynamic load will increase at a geometric rate, as the cube of the velocity?

Application: At the very time you are asking your engine to induce maximum acceleration of the mass of the car, the rotational resistance (rotating mass + aerodynamic resistance) of the engine driven fan is likely to be high and is surely increasing at an increasing rate.

I don't have the engineering skills, the design data or the math skills to analyze these factors. I suspect that the complexity of these questions and the answers are beyond the scope of this discussion. I am comfortable with the statement that replacing the thermo-fan in the rotary with an e-fan will improve engine response to some degree. I suspect it is enough to measure by field test.

Whether the improvement is likely to be worthwhile after considering the negatives, personally I do not expect it to be.

Agreed. I might also do this and put the Gtech to work.

Thank you.

I appreciate the civil and rational technical discussion.

antnicuk

Thanks for all the info, there are again differing opinions but people seem to lean towards the stock fan, mine has worked great and i have been more than happy with it. As mentioned above, i'm not doing it for more power, but more to do with tidying the engine bay, reliability as my fan is 17 years old and if i go for a WOT breaker in the circuit which would be quite easy i think then i would certainly get more more power, even if only a little.

NZConvertible

They did, but that arrangement also put the front of the engine so close to the radiator that a mechanical fan was out of the question. Again, an e-fan solved this packaging issue. It's taken Audi until now with the upcoming A5 to see the wisdom of not hanging the entire engine longitudinally in front of the front axle line.

I don't believe that's correct at all. Air is not being accelerated towards the centre of the fan, which is the definition of rotational acceleration. Nothing is keeping the air attached to the fan so it can't possibly affect it's mass and hence inertia.

The way I see it, it's requires a couple of orders of magnitude more work to accelerate the whole car that it does the fan. I just don't see the fan's rotational inertia having much more than a negligible effect due to its relatively light weight. Plus once it gets to a certain speed it stops accelerating, and I'm not sure how fast it's able to react, but the increased airflow (and hence lower air temp) across the thermoclutch will cause its engagement to drop.

But like I said, I'd rather see real performance testing than endless theoretical debate...