Another but mush easier and quicker Q - when I had factory fans on b4 my main fan died I bent the A/C evap forward a bit so it wouldn't munge my koyo everytime I remove the koyo and I wouldn't have to remove the charge piping to remove the koyo. Now I have the slim fans 2x12" siliconintakes 1500 cfm fans and when I run A/C in hot temps here I see much higher temps than I should.

I have about a 1/2-3/4" gap b/t my evap and radiator and even since added an undertray and the new fans + and oil cooler still see the higher temps - should I push the A/C evap back out so it sits like 1/8" off the radiator or even closer or leave it the way it is ? Any benefit to having it really snug with the radiator ? Seems it would pull air through it better but I do have good cold A/C regardless but tend to get into high temps in the 85+ deg weather w/o heavy boosting when A/C is on? Also what's the cutoff on temps - when should I pull over and shut it off / open hood to cool ? My new gauge starts warning at 209 deg or so but I'm running 60% coolant/ 40% distilled water and a 16psi cap so no more bubbling over in the resivoir ? Just curious about the gap with the evaporator, would eliminating this help ? I have the room now with the slim fans to not have issues removing the radiator easily/quickly if needed etc so I no longer have a need to have this gap anymore..

 

I'd push it back to where it "should" be if it doesn't have any benefits where it is anymore..couldn't hurt right? and if it does just pull it back again.

 

The CONDENSER is affixed in front of the radiator. The evaporator is located under the dash.

Money says you didn't build a shroud for your fans. That's the problem. Search "shroud" and "fans". Welcome.

 

You're 100% on the money though seems most ppl here that bought these fans just strapped them on and have no probs ? I did ask about shrouding in :

https://www.miataturbo.net/forum/sho...ht=shroud+fans

But no one has responded to that. Also I've seen a shroud example in:
https://www.miataturbo.net/forum/sho...ght=fan+shroud
and
https://www.miataturbo.net/forum/sho...ght=fan+shroud

But these are both again using OE fans and or OE shrouds with modified fans in the center.

I have yet to see a single example of a custom shroud or even a sketch of how it would fit ? I take it the idea is to taper off to the fan while covering the radiator surface with about a 1-2" gap b/t radiator and interior of shroud leading up to the fan but this is not what most ppl here are running (at least those using slim fans) - not that I'm at all opposed to fabbing something up don't get me wrong I'll all for a good entailed discussion on this - just want to understand why the use of slim fans when shrouding defeats the purpose ? Also what material would be good for building such a shroud if you don't have the OE's handy ? Is it really necessary when running fans that are higher cfm than stock and they're mounted direct to radiator surface with arguably their own shrouds built in - there's another argument to be had here as to the cooling effect at speed with the shroud becomes less effective (maybe a shroud with flaps that could open at higher pressures could overcome this )? I appreciate the input but just have some more Q's for ya. While the slim fans move more air flow I can't argue with the fact they are def cooling two 12" circles of the radiator and not the whole thing. I take it I should move the condensor closer to the radiator now that it's no longer an issue with clearance removing the radiator? I have to point out also that the 2x12 cover at least 85% of the radiator and pull cooking hot air but the shrouding idea is interesting to say the least - I'd love to see a pict of a slimline mounted with a shroud (other than OE - something custom) ?

Thx,
-B

 

Actually a lot of people ASSume you don't need shrouds but indeed you do. Granted most people installing them just put a huge new radiator in, so sometimes you won't overheat as the radiator is much larger.





When you install the pair of slim fans directly against the radiator with no shrouding, you're doing several things wrong. Mainly, the fan is having to pull a "shell" of air. It only pulls air where the blades are. So no airflow from the very top or bottom of the radiator, the sides, or the corners. However, your fans have a huge circle in the center that the blades are affixed to. No air flow there either. This picture better illustrates what I'm saying. Red is where air can pass through your radiator. Blue is where it can not. It's pretty clear from this illustration that over half the radiator isn't being used.



Now, people install these slim fans because they are "slim" and take up less space than the stock fans. They also are advertised to move more air. However, if you bolt them directly to the radiator with no shrouding, they will actually move less air than the stock fans as the stockers have the shrouding built into them have more area to pull air from. Less air and less area to pull it from is a bad combination. However, I've seen it done many times on this forum.

The best way is to construct a shroud. The shroud will cover the entire area of the radiator and space the fans away so that air can be pulled more evenly throughout the radiator. The further away the shroud puts the fans from the radiator, the better.

 

Cool pict - much thanks for explaining this thoroughly. This gives me a good starting point though I may use thin sheet aluminum instead of fiberglass but I like the general sketch and idea.

Thx,
-B

 

Here's an interesting one:

http://www.fatcatmotorsports.com/fanshroud.htm

-looks relatively easy to make or a variant of it anyway, would need to sit a bit more off the radiator but I like the idea.

 

You can also build a frame and rivet the plastic (or sheet metal) on. This version I built the frame from thin flat stock and then tack welded sheet metal to the frame.

 

Very nice :-) I can see a few tac spots - looks good. Don't have any picts with it off do ya ? So there's quite a few ways to do this and it doesn't have to apex at each fan (makes this easier), taking the rad off and fans off again tho = suck but if it will be a final fix I'm in, I'm not sure if I can get hold of a sheet big enough locally without going to a steel supplier who sells huge sheets (although it looks really nice and steel is much cheaper than lexan) so may have to have a metal frame (with some rubber insulation on the radiator side) and lexan for the flat surface - should still serve the purpose but I'd prefer to go the route you did - tac'ing is MUCH faster, besides it's always fun to weld :-) What thickness of stock did you use - 1/8" ?
-B

 

I did somewhere. It's just sitting on a shelf right now- haven't used it in a year + since installing a different (size) rad. That rad was a griffin that had five rows removed on the pax side to pass an intake (race car). I used it on my street car, but went through a couple of leaks and just gave up on it. Too abused IMO. Don't know if the frame would work on anything else straight up- but it's really just a matter of cutting of the tabs and moving/modding them. The materials used were home depot chain link fence slats and hvac sheet (hold breath while welding).

 

Thats good - def hold breath with galvanized steel - ok so you guys inspired me and I got a couple 2x2 mild steel plates with 1" and 1/2" wide by 1/8" thick bars - will break out welder soon. My only Q is this doesn't seem like a lot of room b/t the radiator and the shroud - I take it the air still makes its way out w/o problems. Should be interesting to say the least.

 

Rolled edges for strength, near 1" depth to get the fans off the rad surface, med. gauge aluminum, and $20 delivered on eBay for 18x26. Cut your fan holes, mount the fans and do some hook type tabs to mount it up. I had this idea a while back and forgot about it. (it's a commercial baking/cookie sheet)

 

So based off of your pict m2cupcar - I fabbed up what I think is a very nice shroud that sits ~1/2" off the radiator and has mounts for the two new slim fans. Lot of tackwelding - lots of inside egde welding but I'm very happy with the results. It's pained now (although I still have to fab the mounting tabs (no biggie) but it sits a good bit off the radiator all sides enclosed (but not too much so it will not interfere with future sways etc) allowing air to get drawn into the fans and fits very nicely on my koyo 37mm. I will post picts prob tomorrow. I have one weld seam in the far right hand side (cause I didn't want to waste a whole nother 2x2 sheet just to seam it in the middle for looks - who cares as long as it functions well). I'm gonna pull the condenser back to the fatory spot and with the two changes I expect I will be golden for southern summer temps. Btw - I added a lexan undertray and it reduced cruise temps by 20 degrees!!! awesome - I still don't' understand where the air goes with the bottom sealed and no vents at the hood but I'm not arguing with success! Thanks for all the tips man - I will post some good picts before I finish assembling it and after.Great advice thanks again! I can post measurements too if anyone else is contemplating building one. I made this with mild steel and ~20 gauge welding quality steel for the 2x2 sheet. Total cost will be ~60$ including stainless hardware for all the nuts/bolts etc. Took about 3hrs (it's been a while since I welded last - but was a fun refresher!).

 

Damn. I should have mentioned to just use some silicone caulk to seal the inside of the sheet metal after tack welding... oops. I think the undertray is less about the air/pressure in the engine bay, and more about preventing high pressure from entering from under the car. Without the undertray, air that's compressed at the base of the nose expands into the engine bay after passing the nose, increasing under hood pressure and decreasing flow through the exchangers. Your lexan is keeping that air under the car. This is obvious with a Miata on track at 100+mph without an undertray as the hood literally swells- you can see the lift.

 

You get nominated for the MacGyver award for that. That's brilliant!

 

Finished - note it was all freehand and yeah I noticed the bottom didn't get 100% covered (piece of steel there was at a slight angle - by the time I noticed was too late). But for not having welded in 15years I'm happy with the results. And yeah these are crappy phone picts. I also moved the A/C condensor closer to the radiator and now my a/c is cold as hell and the car is running cool finally :-) Thx for the tips time !

 

Looks perfect. How does it perform?

 

Okie - shroud and fans in, undertray on - fans running (dual fan mod), condensor at stock distance to radiator - everything looks happy, ~50% coolant mix - all w/koyo 37mm. Hwy cruise in ~90 deg / 80% humidity shows temps at ~185 (I have a 160 thermo and a 16psi cap) w/o A/C on. I can boost the crap outta it and not top ~192 in this weather but at normal cruise with just the A/C on it will overheat within 4-5mins (gauge will slowly climb to 209 -210 and start flashing and I can at the same time watch the factory dumb gauge climb at this point). Turn A/C off and within a min or two I'm back into 190s and dropping WTF ???

How the hell does A/C make the car hotter than heavy boosting ??

Little history on the A/C - I killed one of the hard lines, it was rubbing on the I/C - replaced it along with the dryer (and insulated the line where it wants to rub this time) and I added some lube and refrigerant (no purge - didn't want to pay a shop - they all wanted ~200$ because R-134a is liquid gold here what a joke - it's 8$ a can at wallmart). I had no A/C issues or overheating after that and that was last summer and on stock fans. So I still don't get how running A/C is cooking things ?

Are the stock fans that much better ? All of this originally started when my main stock fan died - so I went the 2x12 x 1600cfm each and now shrouded 2x12 route and still can't run A/C but I can boost it hard ? Bizzare

Thoughts:

-Maybe A/C is low and it's cycling the compressor too often ?
-A/C belt is too tight and causes excessive (parasitic) load when compressor kicks in ?
-I could have a head gasket leak and the strong cooling system is making up for it untill I turn A/C on (I would expect to see tell tail signs on this one - but don't have any)?
-Stock fans are that much better ?

Any suggestions are welcome

TIA,
-B

 

The reason is basically the stock fans pull air more evenly through the radiator than two slimfans bolted directly to the radiator, or in your case, 1/2" away from the radiator. If I were making a shroud, I would space the fans as far away as possible from the radiator. I will probably angle my shroud, as I have little room down low because of the swaybar. However, there's more room up top. So my shroud will be as deep as possible down low (maybe 1-2" max) and taper to maybe 4" up top. Dunno, but the further the fans are from the radiator, the more even they will pull air. I'm not expert, but spacing them a 1/2" isn't doing a whole lot. It should help some, but spacing the fans 2" would likely fix your overheating problem.

 

I'm curious how m2cupcar's should worked out as it has virtually no spacing vs the 1/2" I used. I'm gonna get a used main fan w/shroud and put it in along with my original A/C fan and see what happens.