SR20 E-fan....push or pull, and which side?

[jspaeth]

When I had my swap done, they just put a decent little 12" perma-cool electric fan on the back of the KA radiator.

I honestly don't know which way the air is flowing.

My current fan's bearings are shitting themselves, and the fan wobbles like crazy and is dinging up the radiator.....time for a new one.


Obviously, at speed, there is air flowing from the front of the car towards the back.

So for an e-fan mounted on the BACK of the radiator, what should I be looking for as I shop around?

I am thinking of one of these 2:

Perma-cool 14"....P/N 19114
Turbo Flex® Electric Fans (http://www.perma-cool.com/Catalog/Cat_page16.html)

or

one of the flex-a-lites:

Syclone Electric Performance Fan (http://www.flex-a-lite.com/auto/html/syclone.html)


It looks like on a size-by-size basis, the Perma-Cools flow WAY more even with similar amperages and RPMs.


Any help would be great. How many CFM is sufficient for an SR (considering it may see future track time)?

Can you change the flow direction by just flipping the polarity of the wires? (they say they can push or pull)

Which way do I want to hook it up (push or pull)?


Normally I would spend a lot of time reading and researching, but my fan has really started shitting itself, and I want to buy one of the today, asap.

FYI, if it matter, my current fan is wired into a little box (controller?) and it comes on when the temps get above a certain level.....there is a metal sensor mounted on the radiator too.

[jspaeth]

OK, well I went out and checked it again. Although the bearings are probably wearing a bit, it looks like the main cause was that the "end cap" that holds blade on the shaft must have been working its way loose, allowing room for the blade to wobble on the shaft.

[eklips3]

it all depends on how much you really want to spend on fans. but mind you that it will be a very good investment.

i just have a set of 2 12" fans set up as pushers. i can only run pushers though because there is no room with a RB swap to have a puller setup. the fans have a combined CFM of 1200. It works great for me but my car is a daily driver and i've never tracked it.

changing them from pushers or pullers is just by changing polarity , super easy.

the best setup i hear is to have a puller setup with the fans on the inside of the radiator. I guess the reason why is because the whole front of the radiator is exposed to airflow.

its good that you have a fan controller , you dont have to worry about flipping a switch to turn them on or off ... i know this hassle ... anyways yeah.. keep it , its good.

[jspaeth]

it all depends on how much you really want to spend on fans. but mind you that it will be a very good investment.

i just have a set of 2 12" fans set up as pushers. i can only run pushers though because there is no room with a RB swap to have a puller setup. the fans have a combined CFM of 1200. It works great for me but my car is a daily driver and i've never tracked it.

changing them from pushers or pullers is just by changing polarity , super easy.

the best setup i hear is to have a puller setup with the fans on the inside of the radiator. I guess the reason why is because the whole front of the radiator is exposed to airflow.

its good that you have a fan controller , you dont have to worry about flipping a switch to turn them on or off ... i know this hassle ... anyways yeah.. keep it , its good.


Yeah, mine is mounted on the back side (closest to the motor)...that is better, you say?

I am not sure which direction the air is flowing, i should check.

I guess ideally, if they are mounted on the side closest to the engine, they should be set up as puller, correct?

[bshotts]

I've read a few technical write ups on electrics vs. clutch-driven, and from my experience the electrics (properly shrouded, installed, and wired) perform flawlessly. On that note, because the radiator face typicallys sees much more air flow at speed, ideally you want the fans to be on the opposite side pulling air through. At speed, the fans may not cycle very often simply because of the air movement, but in a stop-and-go situation or repeated heavy engine load, you want maximum air movement from your fans. I have relied on my Flex-a-lite dual 12" fans for years with zero issues, but you have to use properly-gauged wire size for the amp rating of the fans i.e. for mine, the max amp draw required using 10 gauge wire, and drawing power directly from the battery. Using an amp-rated relay to cycle power is also necessary, but good aftermarket fan kits usually include a temp control box that has an integrated relay.

However, because of the initial power draw when the fans first come on, I recommend you pick up a variable speed control box so the fans aren't running at full capacity if all they need to do is supply a small amount of air flow. At full capacity, the FAL can be loud and the older styled fans (like mine) have been known to drone and be noisy, but of course the new dual 12" kits have S-bladed fans that are supposed to be quieter and more effiecient. Keep it cool...pun intended.

[fliprayzin240sx]

Yeah, mine is mounted on the back side (closest to the motor)...that is better, you say?

I am not sure which direction the air is flowing, i should check.

I guess ideally, if they are mounted on the side closest to the engine, they should be set up as puller, correct?

Yes, its supposed to pull. Stick your hand behind the fan and you should feel it blowing the air towards your hand. I've seen folks wire fans backwards and its pushing air. Also, I like mine being on a switched thermo so its not on all the time. Itll only be on when it gets to certain temp. Helps getting it up to temp in the mornings.

[jspaeth]

Thank you guys for your responses. I will double check the fans.

As far as havig a legit car that can see track time, is it absolutely NECESSARY to have a shroud around the fans? I could imagine that would actually HURT airflow at higher speeds, right?

[fliprayzin240sx]

Thank you guys for your responses. I will double check the fans.

As far as havig a legit car that can see track time, is it absolutely NECESSARY to have a shroud around the fans? I could imagine that would actually HURT airflow at higher speeds, right?

Having a shroud helps...ALOT. The whole idea is that you want the fan to "suck" the air thru the radiator. Without a shroud, the fan wont be as efficient.

[jspaeth]

Having a shroud helps...ALOT. The whole idea is that you want the fan to "suck" the air thru the radiator. Without a shroud, the fan wont be as efficient.

Ray, my question was aimed more at "track conditions"

My feel on the "physics" behind this.


At low speeds, the fan is important, and the shroud DEFINITELY helps.

However, I could imagine at fast speeds, when the air is traveling through the radiator rather quickly, the shroud TRAPS air in it and prevents air from flowing through the radiator as fast as it would be able to if there were nothing there blocking it (from behind).

Is my thinking wrong here?

[fliprayzin240sx]

Ray, my question was aimed more at "track conditions"

My feel on the "physics" behind this.


At low speeds, the fan is important, and the shroud DEFINITELY helps.

However, I could imagine at fast speeds, when the air is traveling through the radiator rather quickly, the shroud TRAPS air in it and prevents air from flowing through the radiator as fast as it would be able to if there were nothing there blocking it (from behind).

Is my thinking wrong here?

I think cavitation will help pull the air thru the radiator with a shroud. I dont think a shroud will trap the air, not at the speeds your going. Now we're talking about doing 200mph, then thats the least of your worries.

Get a shroud and duct the fuck out of the gap between the FMIC and your radiator. You want as much air that comes thru the FMIC to go into the radiator and not around it, over or under the radiator. You'd be surprised how much that shit helps.

[Rabboni]

The fan shrouds do not only to make the fans run more efficiently, but they direct airflow across the engine to further increase cooling ability. So, fan shrouds are good for stop and go situations, and high speed situations.

[g-via]

Ray, my question was aimed more at "track conditions"

My feel on the "physics" behind this.


At low speeds, the fan is important, and the shroud DEFINITELY helps.

However, I could imagine at fast speeds, when the air is traveling through the radiator rather quickly, the shroud TRAPS air in it and prevents air from flowing through the radiator as fast as it would be able to if there were nothing there blocking it (from behind).

Is my thinking wrong here?

I did a bit of work in industrial HVAC design.

AFAIK, fans are rated using t.s.p, or total static pressure. It measures the differential in pressure between the high and low pressure sides of the turbine. This is a direct correlation with temperature differential, and efficiency of the fan itself. Having a shroud on the fan creates a higher pressure on the output side (if your fan is pulling), and therefore more efficient.

[jspaeth]

I did a bit of work in industrial HVAC design.

AFAIK, fans are rated using t.s.p, or total static pressure. It measures the differential in pressure between the high and low pressure sides of the turbine. This is a direct correlation with temperature differential, and efficiency of the fan itself. Having a shroud on the fan creates a higher pressure on the output side (if your fan is pulling), and therefore more efficient.

i am a chemical engineer, I understand this concept PLENTY.

NO DOUBT that the shroud helps the FAN circulate air.


however, at higher speeds, the effect of cooling due to CONVECTION due to the air flowing through the air ANYWAY (bc of high speed) dominates any effect that the fan has.

what i am proposing is that a shroud could actually inhibit air flow at high speeds by "blocking" the back side of the radiator.

Did I explain that okay? I think maybe I wasn't clear....