stevej88na

I spent some time today estimating the CFM output of the stock S4 mechanical fan, and came up with some interesting results. Here are my findings:

S4 Fan CFM Estimation

And here's the conclusion, for those that don't want to wade through the article:

So, it isn't necessarily true that after market fans won't reach the CFM level of the stock fan. It's quite the opposite: after market fans tend to be overkill at idle.

Icemark

Reading your article, it fails to take into consideration that the stock fan freewheels at highway speeds and cooler air temps, so a static test won't represent either the aftermarket fan (which if it does not freewheel will actually change the Cd on the car) and the disconnected freewheeling fan.

But your article is a good start.

stevej88na

Good point about the freewheeling at high speeds. I can see how the Black Magic might pose a fair amount more resistance to airflow than the stock fan since the 150's fan and shroud are right against the radiator.

With this article, I wanted to compare the two fans at high temperatures and low forward speed - a classically bad scenario for cooling - to see if the Black Magic was actually worse at cooling than the stock fan when both fans are at maximum output. It turns out it's not worse, but better, at a cost of 1/2HP.

Thanks for the heads-up, I suppose I need to specify that in the introduction!

RETed

There are also PWM controllers that do not run at 100% all the time.
Spal makes the FAN-PWM which has a 50% PWM setting.
Also, I think Black Magic just came out with a variable PWM controller...
This gets around the ON / OFF binary operation for most electric fans.


-Ted

ericgrau

iTrader: (1)

Strange, I got that same black magic electric fan before. It pulled noticeably less air than the stock fan. I popped the hood and felt it. Maybe I'm mistaken and I was feeling the stock fan during warmup, but I don't think so.

stevej88na

Maybe that'll be my next project after I finish the MAF swap (patience my5ababy!), I already have all the components I'd need. That's one thing most current electric fans lack.

Interesting, I unfortunately don't remember how my old fan felt (I swapped in an electric fan before I knew any better - seven years ago), but the stock fan can potentially pull more air at speeds above idle. If this is any reference, I can feel a good breeze when I'm near my rear license plate and the fan's on, and the fan itself is louder than my Toyota Corolla.

Aaron Cake

iTrader: (1)

People keep examining the e-fan "debate" from the wrong angle. Seriously, who cares how much any fan flows as long as it is enough?

The real debate (if you can even call it that) is centered around claims regarding gains in performance. That's easy enough to disprove and really people will keep thinking what they want, even if it is wrong.

The real problem with e-fans is not the fan itself, but the crappy installation that 99% of people seem to end up with. Any advantage the e-fan may have is totally negated by the fact that it might burn the car down at any time...

txfatboy

I have run e-fans on every performance car I have built and each time was for different reasons. The main reason I swaped my T2 to an e-fan was to make working on the car easier. It seemed that when ever I needed to work on my car I was having to remove the fan shroud to gain access or just make the job easier. I had to swap out the front crank seal late last year and it took less than 10 min.
Yes I am a profesional tech and I do have the proper tools but not having to spend an hour removing that shroud made the job much easier.

I have had the e-fan for a while and even in our hotter-than-hell summers in Texas with the ac on (and stock replacement radiator) I never have any overheating problems.

Alex Rodriguez

iTrader: (137)

+1

stevej88na

I wanted to research the widespread belief that "no electric fan will ever cool as well as the stock one" (you know you've heard that). That's the debate I was concerned with, and I think I've provided some solid estimates of the stock fan's CFM, which I've never seen before, which suggest that in fact an electric fan can cool as well, if not better, than the stock fan - at least at low speeds. Though many have known an electric fan can cool just fine, there are many who didn't, because some of the threads and other info spreading around tend to say electric fans are never a good idea.

As for hooking one up properly, RotaMan posted his method here: http://howto.globalvicinity.com/gv_w...=148&co=1&vi=1

As always, to provide the community with the best info possible, if you have improvements or suggestions, please update it.

stevej88na

Here's something else interesting: if the shroud clearance goes from 0.75" to 0.76", the CFM drops by 6% at the same pressure. So, tip clearance is extremely sensitive, and shows yet again that having a shroud is very important.

NZConvertible

An amateur with basic hand tools should have the shroud off in less than 10 minutes. Either you're not a very good tech, or more likely this is just another case of the exaggeration and myth that always seems to be used to justify e-fan swaps.

And this is completely true, because with a healthy thermoclutch the stock fan controls engine temp perfectly. How can any e-fan installation, no matter how powerful the fan is, do any better than that? That's not a rhetorical question either; I'd really like someone to answer it.

In all the e-fan debates I don't think I've ever heard anyone knowledgeable make the blanket statement that "electric fans are never a good idea". I'm sure it's been said many times that crappy electric fans are never a good idea, poorly installed/wired electric fans are never a good idea, electric fans installed by people who don't know what they're doing are never a good idea, etc, etc.

jonesfromindia

ive been driving without a shroud on for about a month, got a new koyo alum rad, they didnt send me the shroud mounting kit for another 2 weeks, and i didnt have time to put it back on till today....

i live in LA, so yes...i sit in traffic, and i drove down to san diego and back up twice.

honestly, according to my stock temp gauge, the temp dropped(on the gauge) was not really worth putting it back on. but there was a difference.

but thats my personal experience.

oh and i want to do the e-fan conversion, i hate hearing the fan over the motor at slower speeds and lower rpms. and i think e fans look better to me. those yellow propellor blades on the fan dont look fantastic either.

another thing.

i totally agree with aaroncake. if it gets the job done, why not? the fact my car could catch on fire at any given momment makes me feel like james bond!

TehMonkay

iTrader: (-1)

I would like to have an efan and electrix water pump setup and an electric oil pump to use on the turbo. No need for a turbo timer, just get these three things to run for a few minutes after shutting off the car. Plus if you overheat or want to cool off at auto-x without wasting fuel you wouldnt have to, just an idea though

stevej88na

True, but I didn't mean it to be taken that way; if I can revise my statement, I'm sure you'll see it's in the spirit of my article:

I should make it clear here, as in the article, that the stock fan can pull more air than reasonable electric fans. The difference is, the stock fan can only pull more air at high engine speeds, and not at idle. One situation this might come into play is driving up a steep hill on a hot day (low driving speed, high engine speed). In that situation, an electric fan might not provide enough cooling capacity. The stock fan can reach 2,600 CFM at 4,000 engine RPM, while the Black Magic 150 is limited to 1,700 CFM.

The trouble is, readers tend to take different things away from those debates, and I've noticed a trend towards thinking electric fans cannot provide the airflow that the stock fan can. Annoyed that no one actually knows how many CFMs our stock fans pull, and in my continued quest for data mongering, I wanted to provide us with some estimates. I found the results somewhat surprising, because when I started out, I expected the data to tell me it was time to put my clutch fan back on.

Another interesting and unexpected finding was the stock fan's shroud. Since it has such a large clearance, its efficiency is quite low. That large clearance alone makes up for the efficiency handicap forced on electric fans. For instance, if the shroud gap were reduced to 0.2" (the gap on my electric fan), it would pull 50% more CFM at idle. So, reasonable electric fans can potentially be more efficient than the stock fan.

With this information, it seems to me that an electric fan fitted with a PWM controller that can follow the stock fan's CFM vs. temperature profile might be a good alternative to the stock setup. You might say, "if it ain't broke, don't fix it" - but I happen to already have an electric fan, so a PWM controller is in my future.

As an aside, HAILERS suggested designing a low-cost digital rotary compression tester a while back (as I've done with some other projects listed here), so I'll be doing that or a PWM controller as my next project.

My electric fan is still pretty loud...

Though we can install an electric fan and see that it doesn't overheat, I wanted to find out what Mazda thought "enough" was. Now we have some estimates to base things off of, can rest assured that the electric fan can handle most situations, but are aware that sometimes electric fans may not be enough. I guess I have to watch the ol' temperature gauge next time I drive up the grape vine!

NZConvertible

Removing the shroud dramatically lowers the fan's efficiency, meaning it has to run far more often than with in the shroud place, which will obviously make more noise (as well as probably using more gas). So you're creating your own problem.

And in you think an e-fan conversion will eliminate fan noise, you can't have heard many e-fans running.

Your fan is yellow? It should be white.

The turbo is water-cooled; you don't need a turbo timer unless you're dumb enough to abuse the car right before shutting it off. Besides, a turbo timer would cost about a tenth of what those three items combined would cost.

ourxseven

iTrader: (1)

I've strongly considered the efan mod recently , but responses from those with over 10,000 posts (and none in the lounge ) gets my attention

i'm sticking with the stock fan and shroud ( it is a nice tool holder)

matthewromeril

I bought an electric fan kit fitted it to the rad it worked great.
After a few small events it was time for the main rally.
What i didn't know was that under heavy breaking and with the fan not bing verticle it slowly broke down the mounting pads.
After 4 stages the fan started chewing into the rad. First i new about it was the coolent warning and the buzzer comming on by the end of the stage it was too late i needed a rebuild.
A very expensive mistake and to be out after 4 stages gutting.
be very carefull i'm a good amature my car is very well put together and i f!!cked it up.

My5ABaby

iTrader: (7)

Mine's a dirty white (kinda yellowish from dirt). But if I clean it the blades should be white.

ourxseven

iTrader: (1)

i'm going to paint an " E " on my blades just to win both sides of the debate

jonesfromindia

Your fan is yellow? It should be white.




its like maybe a neon greenish yellow. positively not white. its not even dirty.

the rx7 gods must have cursed me white ugly blades.

and my civic e fan, i had two, were no were even close to hearing in the car.

stevej88na

Ha! You can tell people that your "e-fan" cools just as well, if not better, than the stock fan in every way. People will PM you incessantly to find out which fan you have. (humor)

^ bonus points to whoever knows where I got that unique parenthetical technique

My5ABaby

iTrader: (7)

Hailers. Do I win?

stevej88na

Yup, you win. I usually find the fact that he's pointing out when something's funny funnier than the joke he's pointing out. But I digress!

Unless my friend from New Zealand has more to say, all I have left to add is this:



I added another data point to the HP graph, and added another that's CFM vs. engine RPM. That's CFM when the stock fan is fully engaged (80%, above 85C).