Here is the control box.

On the top you have the 3-way switch for On, Off, and Auto. The two wiring looms go into the box and end in connectors, the top comes off to access. Inside are the relays, the diaodes, the fuse, and a bunch of wire.

 

and the whole thing from the front.

 

Here's the first two pics in-line

8" Fan and thermo switch



And the control "Box"



I forgot to dust before I took pics :-)

 

Let's see if I can translate...

Both can flow the same rate, but one takes less amperage (electrical power) to do it. I believe, however, that this can have an effect on the following...

This means that if there is the slightest positive pressure on the side that the fan is trying to force the air into, flow rates drop like a rock. When some flow ratings list the cfm at zero pressure, that means that the fan will flow that amount in still air, with absolutely no obstacles in either path. I think if a fan is more efficient, it can overcome those obstacles better.

If the pull-type fan is mounted flush against the IC core (no stand-off/shroud), air is pulled through a circular area that is full of small air passages, so a vacuum-- and thus, a "pressure drop"-- is created. This cuts down on the flow rate.

In order to keep the flow rates up, you need to mount the fan just above the IC core, so that the pressure drop is less. But you will get less flow through the core as well, so it's a compromise either way.

A shroud will ensure that you're making the fan as efficient as possible, but you need to "stand off" (mount it above the IC core) a bit to prevent excessive pressure drops.

But since there's not much airflow through the IC core and piping when trolling in traffic, plus the heatsoak from the underhood heat building up on the intake manifold and IC piping, don't expect a big drop in temp numbers at the intake air temp sensor on your PFC Commander.

It's better than nothing and letting your IC heatsoak to death, however. And any temp reduction you can do while sitting will pay dividends when airflow ramps up at speed, and the IC can do its job.

Hope I did OK, KevinK2.

 

KevinK2: Why would you say "make sure rad fan is on at low when IC fans are on"

It doesn't hurt to have them on - that's for sure. But I stumped at how it can hurt to leave them off. The other way is defineteley true - you want the IC fan on any time the rad fans are on, or else you will get hot air flowing back through the IC.

But for the IC fan, who cares if a little 130 degree air is flowing through a 190 air/water radiator that won't heat soak. That would actually be better than no air.

And if the other points in this thread are valid, the rad fans could cause a litt e problem, because they move so much air that the pressure goes up a bit, and that makes more work for the IC fan.

Or am I missing your point entireley

*waiting to be told I missed the point*

 

On reading Kento's mail, I'm wondering if the SOUND the fan makes would change if the fan housing is offset away from the IC a little bit. Can someone that hasn't already locked theirs in give this a try while installing?

If Kento is correct, then the higher pressure drop could cause more sound. The one thing I'm not crazy about is the Hairdryer sound my 8" IC fan makes. From the pics above - you can see I have very little gap. If the sound does not change then maybe there is pretty good flow the teh IC already. ??

 

Kento, I am slow so please clarify for me please.
The fan or fans (in my case two 8 inches) should be off the IC core slightly to create a higher pressure drop and help in cooling, rather than having the fan frame flush against the IC core???

 

Kento - I follow you and agree with everything you said - except the point about the higher efficiency fan being able to adapt to more resistance. I'm not sure that is true. It is conceivable that a fan with the same cfm but higher amperage is designed to stay at its cfm range at higher resistance by design.

I am just guessing - as I am still hanging by the belief that motor design has changed little in the past 10+ years atleast. Further the SPAL I bought actually publishes the CFM's given the pressure where I haven't seen others
well except Davis Craig (nice) and I can't find them in the US. http://www.daviescraig.com.au

who knows..

 

If I'm reading KevinK2's reply correctly, yes, you don't want them mounted flush against the IC core, but not to create a higher pressure drop-- you want less of a pressure drop, in order to keep flow rates up. According to the SPAL chart, once the pressure drops reach a certain level, flow rates go down. But you need to have them close enough to create airflow through the core; so it's a compromise.

 

I'm just guessing too. But my line of thinking is that different motor and fan setups require varying degrees of current draw to function efficiently. I'm thinking that a larger cfm/lower amperage unit would be better able to maintain its flow rates due to better efficiency. But I could very easily be completely wrong.

 

FWIW the fan mounting kits from Summit Racing do come with 1/2" rubber spacing blocks.

 

Tried out the new fan setup last nite, wired a switch into the center console to run it.

Strange results kind of. Intake temps seemed to actually rise *faster* at idle with the fan on. But then when I got moving and left the fan on they would drop much faster too. Temp was only 60F or so too and i saw intake temps into the low 50sC (about 120F)

My IC duct isn't sealed for squat so like LUV thats my first order of business. But by holding a bit of paper in front of the ic duct i can tell the fan is pulling air through it so hopefully this is at least on the right track...

fwiw, the 7.5" fan moves a good bit of air *for its size*. Also noticed that the fan motor gets pretty hot, but then so do the rad fan motors.

 

Kento wait, I am more confused now, unless SEMANTICS is playing games with me.
If you want pressure to drop behind the IC core to help increase flow or speed of air thru the IC (vaccum effect), the higher the drop(read lower pressure area behind IC core) the more vaccum effect, the better cooling ability because the increased flow.
The air wouldn't have to fight that pressure area to go thru the IC core.
On the other hand, the lower pressure drop(read pressure drops not so much) then there is a less of a vaccum effect behind the IC core, so air has to fight that pressure area in order to flow and the less flow the less cooling ability.
Right??

 

Airborne, you are not alone.
I have that same strange effect on idle, the intake temps increase faster but also cools faster once I get moving.
My IC is well sealed and the shroud nose, I extended the length so as to incease more the pick up of air flow from the front.

 

RRA- what did you use to extend the shroud? i would love to widen it and move it farther forward.

I'm headin toward home depot racing today to check out some options.

 

Airborne, I got from Lowes Racing Team one thin aluminum sheet that I could bend easily and cut it out in the size and shape to what you want it to do.
Still no change that I can tell a difference.

 

Seems to make sense - the fan will pull air from the path of least resistance. Out of curiousity how thick are your IC's - as thick as the greddy ~4". - I'm thinking it is best for me to have my fan up close to help pull air through the 4" of IC. If it was thinner I'd agree that I should use a standoff to help velocity and create a vortex in the middle of the fan area.

Hopefully with the 4" of IC - the fan uses the duct air rather than trying to suck back through the backside of the IC.

Seems that a vented hood is going to still be required to eliminate the pressure and hot air in the bay.

 

RRA- I've heard of LRT, good stuff . What did you use to secure the aluminum to the duct, some sort of glue/tape/etc???

 

"and at least for dual 8" fans, make sure rad fan is on at low when IC fans are on"

with dual 8" IC fans, I think the back flow thru the rad would fill the snout with hot air, which is where the IC duct inlet is. don't want preheated air fed into the IC. As u noted before, if u just have a single smaller fan (typically flush mounted) the flow may well be low enough to not have any significant recirc thru rad, so no need to run rad fans in that case. the increased pressure under hood from having stock fans at low should not be an issue with dual 8's on the IC.

---------------------

good clarification on my post Kento.

since Ken has temperature probs, mabe he can test the effects of using rubber washer standoffs on both noise and cooling.

one reason IAT sensor temps may not drop much with IC fans at idle is that the increase airflow under hood increases hot air flow across the intake manifold, increasing it's temp. increased heating of the air in the manifold may offset the extra cooling that happend in the IC. just a theory.

seems like several noticed quicker cool down of IAT once motion was resumed, likely due to core precooling.
question is could you feel the difference, and is it worth doing? The earlier link for the ford supercharged coupe was interesting, but note 400F exit temps from the sc at 15 psi imply a horrid 30% compressor efficiency. The gains he documented were for very, very hot initial charge temps.

for auto-x or drag racing, the IC fan(s) and (if legal) a water spray for the inlet duct, would be a great way to precool the smic core mass before a run.

 

Yes, but you're forgetting the whole cfm/pressure drop conundrum. Remember how the fan's rated cfm drops like a rock when the pressure drop increases? What's happening is that even though you're creating more of vacuum that is "pulling" air through the IC core, the airflow rate or speed is slowing down drastically; you're actually moving less air through the core per minute, because you're exceeding the fan's efficiency. Trying to move air through all the small passages in the IC core slows the airflow rate, and it requires more and more work from the fan unit as the "vacuum" increases. As seen on the cfm/pressure drop chart in the SPAL link, the actual amount of air a fan can move per minute decreases by creating too much of a pressure drop. It's a compromise; you want to create a good pressure drop to "pull" air through the core, but you want don't want to exceed the fan's efficiency (since you can't really control the fan's actual speed), which would otherwise slow the airflow too much for efficient cooling.

This is why the rad fan motors are so huge comparatively. They need that power to keep their efficiency ratings high enough to avoid slowing the airflow rate.

Wakari mas?

 

Airborne, I took out my IC shroud and extended the nose of the intake and used 3 screws with bolts to hold it in place. The bolts need to be very low profile so as to clear the radiator on the way back to its place.

 

I fixed my should. The outside air temps were 70, I put the thermometer after the IC at idle and it read 120F degrees after the fan. The thermonmitor after the IC read 90F Degrees. So the fan was sucking 30F degrees off the IC.

It's only 27% of the surface, so I don't expect drastic redutions.

My guess is it reduced air intake by about 10F degrees at idle and standing still.

My Omega guages are not accurate for this test. I will be talking to them in the future.

My main concern to that the PFC, Commander is really slow in displaying the intake air temps.

My concern is if my car was tuned with these temps in mind, them maybe the tuning is not accurate.

Ken

 

Luv94rx7 - you should read this thread...

https://www.rx7club.com/forum/showth...hreadid=142819

 

And I thought we were so cool with our esoteric discussion about air flow, pressure drop, vaccum.......etc.
This threads makes me feel like a Moron (not that I said I wasn't one).
Darn those PFC experts!!!

 

despite all that higher thinking i'm forging ahead with my shroud sealing and duct expanding.

here is duct v.1. i just extended the pettit duct downward. it did seem to speed up cooling when moving. or maybe it was because i sealed the shroud.
did the guys with the pettit cc2 notice the shroud doesn't reach the bottom of the IC? i extended it with some aluminum.

duct v.2 will be enclosed on all 4 sides. the fan is definitely pulling air in but seems to be finding some hot air too.