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Should Myron make this fan shroud for us?

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I posted this on the forums last week, but it was pulled down because the post appeared to be a group buy(even though it wasn't). Anyhow, I am posting here again because this fan shroud is VERY slick looking(CLEAR polycarbonate!) and functional and I think we can pursuade Myron, aka 2/3rdsCobra to make them for us, however right now he does not think there is sufficient interest.

Basically, I am trying to get some interest going for his fan shroud because I have seen it in person and I think it would be an awesome product that many of us could use - I know I sure will need this once spring hits. Myron showed off his fans and shroud setup @ the BAMA tech talk a few weeks ago @ PR Motorsports in Hayward and I was amazed not only how nice it looked, but that it worked so well. Even with his hood open the air flow being sucked into the radiator and intercooler was amazing. I put my hand about 1/2 a foot in FRONT of the mouth of his bumper and I could feel the air flowing in :p

Even if you have high flow fans like Spal's or the like you are NOT going to be able to maximize the cooling efficiency unless you have a properly designed fan shroud. Without a fan shroud the corners of the radiator will have virtually NO air flow. Also, an improperly designed fan shroud is even worse as it will hinder air flow at speed. I have seen Myron's fan shroud and it has sufficient space between it and the radiator that this will not be an issue. ALSO, if you have an AC condenser and/or an intercooler that sits in front of the radiator then airflow at speed is moot - the air is almost completely BLOCKED by the IC and/or air conditioner condenser. At most 30% of the radiator will get cool INdirect airflow so IMO having a fan shroud is a MUST for anyone that is running forced induction or someone that does track events or mountain runs and has AC or an intercooler in front of the radiator.

I have thought a lot about this and I really want Myron to think about making these for the community. PLEASE PM him to show your interest or ask him questions - he is very knowledgeable and even if he does not make these shrouds for the public he would likely help you build one for yourself - I am hoping it does not come to that because I suck at fabrication :roll:

Here are some pictures:








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I've talked to him already.... and I'll most likely be getting him to make me one... as I really need something b4 spring hits... wonder if he could offset my fans just a bit toward the passenger side for extra clearance
 

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Trick piece, though I do wonder how you can get it any closer to the radiator (to make a better seal).
 

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I have received a number of PM?s and e-mail?s regarding the necessity of a shroud and the effectiveness of this set-up compared to fans only. Companies like FM have sold an upgrade for the OE fans for years and have not offered a shroud, so why is one needed now. Further, some very knowledgeable people in the industry, whom I respect, have mentioned that having a shroud will actually impede airflow and thus reduce cooling ability of the system in total.

This is believed because the shroud blocks airflow through the core and out of the radiator, creating turbulence in the areas blocked by the shroud and in some cases, air reversion between the shroud and the core. If this was the case, this would not be good at all. This would make the radiator act as a heat sink in the areas the shroud blocked.

So, I did a test to prove or disprove my position. I videoed this test and posted it on the url below. Suffice to say, I was right  Even with the enhanced air speed of a leaf blower (rated @180 MPH air speed) right up against the IC core, there was only about 10-15 MHP of air coming out the back side. There is more air speed and volume when you blow across your soup spoon to cool off your chili than what came out the back side of the core. This isn?t even taking into account any efficiency losses from heat transfer from the other heat exchangers (in my case the IC and air conditioning condenser).

I have found that the fans are the PRIMARY source of airflow on the Miata, not the high speed run on the back straight or on the freeway. As such, you will get more benefit from the fans if they are drawing air across the entire core (by use of a properly designed shroud) then by having them strapped to the core directly. Secondly, even if you have no heat exchangers in front of your radiator (Spec Miata?s) there is only about 30% of your core exposed to the high pressure air. If you decide to lop off the front end of your Miata to expose the core, then the shroud won?t be needed. I like the front end though, so I?ll be keeping mine.

Anyway, enough of my rambling, so, here are the vids. Please don?t be hypercritical of the editing or narrative (I did this off the cuff) of the video, but just the content. Hit part one then part two. This was filmed on a Canon A70 Powershot, so I had to split the video to get a bit better quality.

http://www.vidilife.com/index.cfm?f=profile.main&intUserAccountID=9492
 

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First of all I appreciate you willingness to test your device, but I think that the experiment is wrong.

The reason is that the leaf blower has a very aimed beam, as a result you don't simulate the actual conditions.

I saw the pictures of the shroud and it might be useful in every day traffic but when the car run fast it will create a restriction...

I personally want maximum airflow when the car is running fast that's why I spent my money for an extractor hood through a GB here...
 

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Discussion Starter #7
I saw the pictures of the shroud and it might be useful in every day traffic but when the car run fast it will create a restriction...
Do you have proof of your above statment? This is exactly why he performed this test - a lot of people believe shrouds inhibit air flow @ speed, but if there is blockage in front of the radiator then how much of the air actually passes through the radiator? As crude as his test was it seems quite logical to me. He put the leaf blower exhaust directy into the mouth and you could see how little air flow there was with the fans off. I suppose he should get one of those big a$$ floor fans that the smog shops use to cool off the cars on the dynos, but I seriously doubt there will be any difference in the outcome.

His comment of "lopping off the front of the car would eliminate the need for a fan shroud" is logical. The issue is the obstruction of air flow into the front of the radiator by an AC condenser and/or intercooler seriously inhibiting air flow THROUGH the radiator. Fans do the work, not the air flow into the mouth. Without good fans you would overheat for sure, even if you had NO heat exchangers blocking the air flow into the front of the radiator, BUT he shroud allows the fans to perform at their best and to extract the heat from not only the circumference of the fans, but from the entire back side of the radiator, which is substantially more surface area.

I would love to see some extensive testing in a wind tunnel and show the effects of no blockage in front of the radiator (no AC condenser or IC), but it's moot (for me) since I have an IC and an AC condenser and I don't plan to remove either of them anytime soon 8)

Also, IMO unless you have nothing in front of the radiator you should create a custom belly pan that butts up directly to the bottom of the radiator so that all air flow is forced into the radiator, but that opens up another question - what effect would that have on air flow past the bottom of the engine and past the trasmission?

Lots of variables and what if's in my mind, but I think fan shrouds are a must for those of us with AC and/or IC's that need to maximize cooling.

I am also sold on heat extractor hoods(well designed one's anyway) and Evans NPG coolant - Myron and Jason C talked me into the Evans coolant - good stuff.

Thanks for the vids Myron! =D>
 

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First of all I have nothing personal with 2/3cobra... I just said my opinion.

The problem with his design (which I believe it won't make any difference even in traffic) is that the round plastic frame of the fan sits on the rad restricting the flow of air only though that area. Am I the only one that see this?

So basically shroud blocks the rest of the rad and doesn't allow it to work...

If you want to design it right you need to let some space between the rad and the fans should flush with the surface of the shroud...

If you notice that's how the plastic is around the stock fans...
 

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Btw the experiment totally cheats since it provides a small beam the goes through the effective area of the shroud ...
 

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If you want to design it right you need to let some space between the rad and the fans should flush with the surface of the shroud...
Look closely at the pics. There is some space between the shroud and the radiator core! The shroud isn't flush...unless you mean there should be more space than there is with the present design. I think it's about 1/4" from the pics. That's about ideal...you don't want the fan to be too far back.
 

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Max_Power,

I appreciate your comment, however in this case, your incorrect. Not that that's a bad thing as I can't tell you how many times I'm incorrect in matters dealing with my wife :lol:

The "small beam that goes through the effective area of the shroud" is EXACTLY what I was looking to get. Airflow measured @ 180 mph, going through 3 heat exchangers (IC, A/C condenser and radiator) comes out of the back end @ only 10-15-mph. You blow with more force and volume across your soup spoon to cool your chili. The fans become the PRIMARY source of air so there is no back pressure or reversion because there in not enough air speed or air mass to be blocked by the shroud.

This means is that there in NO high pressure air that hits the radiator core and therefore the shroud. In my case the only heat exchanger that is getting any benefit of high pressure air is the IC. If you believe that 30-40 mph air (estimated air speed @ front side of the radiator core) on 30% of your core is enough to cool your coolant, then more power to ya.

Greg G, the shroud, based on it's thickness sits the fans back an inch and a half from the core. Actually, if you have a fan capable of flowing large CFM, then putting in farther back is ideal. If I could build the "perfect shroud" for the Miata, sans no space/size limitations, I would set the fans back about 10-12 inches from the core, radius the shroud back off the core and angle the fans up towards the hood (in my case vents) to blow the heat right out. Of course, this is impossible given the space available, so this was the next best thing.
 

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I might have missed something, but who makes these exactly?
 

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If you want to design it right you need to let some space between the rad and the fans should flush with the surface of the shroud...
Look closely at the pics. There is some space between the shroud and the radiator core! The shroud isn't flush...unless you mean there should be more space than there is with the present design. I think it's about 1/4" from the pics. That's about ideal...you don't want the fan to be too far back.
Not that's not what I mean Greg.
You see the air inside the shroud cannot be sucked by the fans because the fans are flush with the rad.
Sure some air it does get sucked from the tiny gap between fun and rad but this is way far from the ideal...
Furthermore there is a gap at the top this should be closed to be more effective.

The shroud does make a restriction in the flow of air. The restriction is applied at the area that the shroud is blocking...higher pressure is getting built up at the rear and the flow is reduced.
In order to simulate the conditions you need a couple of big fan in the front of the car and many smaller pieces of tape around the back of the rad...still would be difficult to measure the difference in the amount of air that is going through since you will have smaller opening and as a result higher pressure - but still the amount of air would always be smaller.
I believe an engineering analysis (from a physics stand point) can help you can help see what I'm saying...

Anyway I'm not trying to sabotage your group buy...I'm just stating a few things (that are very obvious at least to me) so you can improve your design...
Currently IMHO is bad - so basically you are loosing the (natural) cooling in high speeds while you don't get any big benefits in the lower speeds.

Just my $0.02
Chris
 

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snipped a bit -
You see the air inside the shroud cannot be sucked by the fans because the fans are flush with the rad. Sure some air it does get sucked from the tiny gap between fun and rad but this is way far from the ideal... Furthermore there is a gap at the top this should be closed to be more effective.
There is about 1.15 inch of space between the shroud and the core and add in .38 inch for the thickness of the material brings the fans back away from the core about 1.53 (one and a half) inches, about the same amount space between the OE fans/shroud (yes the stock fans have a shroud of sorts) and the core. Since the shroud is clear polycarbonate, it looks as if the fans are right on top of the core. This is not the case. I could have used aluminum, like AWR, but in order to get aluminum sheet as rigid as this polycarb, I would have to have a heavy piece (not good) or use an old "hotrod" trick and channel the sheet to enhance it's rigidity. That would have added to my cost, plus I have a bit of background in plastic forming, so polycarb got the nod. Another benefit to using the polycarb is it's impact resistant, aluminum is not, so if your are pulling off boost tubes and you hit an aluminum shroud, oops, sorry you now have a dented shroud. That won't happen w/ polycarb, although it can be scratched, it can also be polished out w/ plastic polish to be made to look as good as new.

Further, There is no gap between the shroud and the core, at all. I used a rubberized foam to seal the edge of the shroud to the core. If you look closely, you can see it. I even mention it in my video and point to it @ the top of the shroud/radiator.

The shroud does make a restriction in the flow of air. The restriction is applied at the area that the shroud is blocking...higher pressure is getting built up at the rear and the flow is reduced.
In order to simulate the conditions you need a couple of big fan in the front of the car and many smaller pieces of tape around the back of the rad...still would be difficult to measure the difference in the amount of air that is going through since you will have smaller opening and as a result higher pressure - but still the amount of air would always be smaller.
I believe an engineering analysis (from a physics stand point) can help you can help see what I'm saying...
Dude, I guess you can lead a horse to water.... there is no high pressure air getting to your radiator core if you have another heat exchanger in front of your core. If you find a way to get the same air speed and volume hitting your radiator core after going through 2 diffrent heat exchangers, you'll need to set up an appointment w/ a patent attorney because you will have found a way to defy a number of fluid dynamic priciples, most of which are beyond me.

You suggest using a high flow fan to "simulate the conditions". I'm assuming you mean like the ones used @ a dyno shop. Most of those fans have air speeds in the neighborhood of 50 to 80 mph. Some high dollar shops have fans that have air speeds that reach over 100 mph, but those are a bit rarer. Even so, I used a fan that delivered a concentrated air speed of 180 mph. If @ 180 mph there is only about 10-15 mph of air coming out the back end of the core, how would less air speed prove your point of high pressure. If you start out w/ less pressure, you end up w/ less pressure following the same procedure I used. There may only be about 5-10 mph of air exiting the core with less air speed coming in.

If you are believe that I had the nozzle pointed so the air hit the shroud and not through the opening which gave a skewed test result, I moved the nozzle around to ensure that it was directed to the fan opening.

Anyway I'm not trying to sabotage your group buy...I'm just stating a few things (that are very obvious at least to me) so you can improve your design...
Currently IMHO is bad - so basically you are loosing the (natural) cooling in high speeds while you don't get any big benefits in the lower speeds.

Just my $0.02
Chris
First, see above regarding your "high pressure" belief. Finally, THERE IS NO GROUP BUY. I designed this fan shroud because AWR kept giving me the run around when I was trying to buy one from them. I kept leaving messages @ the shop, but no one would get back to me. When I was finally able to talk to someone, I was ready to buy w/ CC in hand. I was told that they didn't have any right now and it was not likely that they would make any soon as they had other more important projects going and the Miata was not that important now (their words not mine). So, w/ that attitude, I decided to build a better mouse trap. You need to remember that I didn't make this set-up to sell, I made it for me. I'll be damned if I would make or put something on my vehicle that didn't offer some type of benefit. In this case, a much more functional and capable cooling system.

A few other people have expressed interest in the set-up and I have agreed to make it as long as I can justify the cost. I still have the .dxf file and the fan source. To toot my own horn a little, I do have a background in automotive performance design and fabrication as I used to own and operate MidKnight Motorsport, a VAG Tuning company. If you can pick up a copy of European Car magazine (Dec, 2000 issue) you will see a write-up on one of my products, the Air Bath system which was a one of a kind open element ram air kit for the A3 and A4 VW. After I sold the molds/jigs and closed the business, another company took one of my other product names for their own, the IceBox system, which was a ram air system for the OE airbox for the same type vehicles. Recently, I have also "assisted" FM and Quaife in bringing a performance gear set to the Miata market.
 

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Discussion Starter #15
Pass the koolaid Max! :lol:
 

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Hi 2/3Cobra my apologies but it just looks like the fan flush the rad if that isn't the case the design is not bad...
Btw the optimal case would be if the bottom of the fan is flush with the shroud but I doubt if there would be space for that...

What I said about restricting the airflow is the rule of all the shrouds (AWR or whatever)...but you have better airflow when the fans are working... ;)
 

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My objections:

First, The only time you should be relying on your fans to cool your car is when you are stuck in traffic or moving slowly. Why don't you set up a light that comes on in the cockpit when your fans come on, I doubt you will see it much if you keep your speed above 30. Did you experiment to see if your fans are on less with this modification?

Second, I don't see you stating anywhere that this increase the pressure differential across the heat exchangers. This is what keeps your car cool, speed and volume are results of this. Chasing speed an volume with out understanding this will lead to a poor design.

Third, when a car is moving pressures change all over the car, you haven't seemed to take any of this into consideration. In these cars the air pressure under the car will affect the pressure differential across the radiator. Why? because the air that goes through the grille can really only exit though the bottom of the car.

Fourth, it takes time for the heat to move from the radiator to the air passing through it, there is a science to making the air move at the correct speed to make this most efficient. Your obsession with air speed is incorrect.

Fifth, what the hell are you doing using a 180mph stream of air to test the heat exchangers on your car? You do realize that most miatas never see north of 100, and that Mazda more then likely designed things to work more efficiently at lower speeds. A low volume stream of high speed air is the exact opposite of what the radiator will see in day to day use.

Sixth, The design of this shroud is poor in aerodynamic terms. You are asking a good amount of the air to make a 90 degree angle when it hits the shroud then another 90 degree angle to exit though a fan. This is going to create resistance and increase pressure behind the radiator lowering the pressure difference across it reducing the maximum volume it can flow. This will get worse as vehicle speed increases.


So all in all this mod really does nothing to address the primary limiting factor affecting the cars' cooling ability.
 

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My objections:

First, The only time you should be relying on your fans to cool your car is when you are stuck in traffic or moving slowly. Why don't you set up a light that comes on in the cockpit when your fans come on, I doubt you will see it much if you keep your speed above 30. Did you experiment to see if your fans are on less with this modification?
Not. If you believe this, I have some fertile farm land in Death Valley I'm trying to unload :lol: . I have done a number of simple experiments to validate this shroud design and fan choice. I chose to video this one as it was the issue most often brought up. FWIW, this set-up did reduce my coolant temp over 8c while @ load (183 KPA) traveling between 50 to 100 mph vs no shroud OE fans off. If fans didn't matter, there should have been no decrease in coolant temp @ speed. Additionally, if there was high speed flow obstruction by the shroud, regardless of having the fans off or on, the coolant temps should have increased. They didn't obviously. Further, with my set-up, I have a residual temp drop (after the fans have turned off) of 6c on average showing that I am getting even cooling across the entire core as opposed to just the circumference of the fans. The temps were measured @ OE location w/ datalog lab via LINK.

The one test I videoed only dealt w/ air speed loss when going through heat exchangers (in my case two of them). Air mass and heat transfer via convection was not calculated into this because I was only showing that air, @ a known speed (in this case 180 mph) was not getting to the radiator core w/o a major loss of speed because of the heat exchanger obstruction. My video proved that there is no delta p @ the radiator core. At the first heat exchanger, OK, but not @ the core, in my case.

Second, I don't see you stating anywhere that this increase the pressure differential across the heat exchangers. This is what keeps your car cool, speed and volume are results of this. Chasing speed an volume with out understanding this will lead to a poor design.
Again, because this was not calculated as it has little to no bearing on whether or not this set-up works. The only pressure differential is the loss of delta p @ the first obstruction (heat exchanger).

Third, when a car is moving pressures change all over the car, you haven't seemed to take any of this into consideration. In these cars the air pressure under the car will affect the pressure differential across the radiator. Why? because the air that goes through the grille can really only exit though the bottom of the car.
This is also addressed with the OE underbelly pan. As you noted there have been many experiments to validate it's usefulness.

Fourth, it takes time for the heat to move from the radiator to the air passing through it, there is a science to making the air move at the correct speed to make this most efficient. Your obsession with air speed is incorrect.
Not, see my response to your second moot point. Air speed through the core is governed by core design (fins per inch & thickness of coolant tubes are among some of the ways air flow is controlled), not by air speed entering the core via fans or natural air flow @ speed.

Fifth, what the hell are you doing using a 180mph stream of air to test the heat exchangers on your car? You do realize that most miatas never see north of 100, and that Mazda more then likely designed things to work more efficiently at lower speeds. A low volume stream of high speed air is the exact opposite of what the radiator will see in day to day use.
Actually it's a high volume (cfm), high speed stream of air. That's why I used it for this experiment. A Miata will never see this much air velocity or mass going through the IC, a/c condenser and radiator core. Now, ask yourself, if @ 180 mph I was only getting 10-15 mph air coming out of the back end, how much air really is coming out the back of the radiator core w/ the air speed and cfm one gets by driving. Not much. In my case definitely not enough to cool the coolant while the engine is in load (above 10 inches of vac and above).

Sixth, The design of this shroud is poor in aerodynamic terms. You are asking a good amount of the air to make a 90 degree angle when it hits the shroud then another 90 degree angle to exit though a fan. This is going to create resistance and increase pressure behind the radiator lowering the pressure difference across it reducing the maximum volume it can flow. This will get worse as vehicle speed increases.
Look, what in gods name does aerodynamics have to do with anything that won't see HIGH PRESSURE AIR? We are not dealing w/ lift or down force. If you mean that there is reversion or back pressure or eddy currents or static pressure between the core and the shroud that will reduce flow it's not there. If you had your radiator sitting out in the open w/ the whole core exposed, then yes, I agree, you won't need my shroud. Also, can the shroud be of a better design, yes, but with the space limitations of the Miata engine bay, this is the best anyone can get.

I proved my point and videoed it to show everyone that the popular belief of "high pressure" cooling off the coolant @ speed w/ heat exchangers in place isn't so. I also invited people to pose questions to challenge me but not to lambaste my design or take pot shots. If you want to continue believing the world is flat, you just go right ahead.
 

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All I can say is, whoever can build a better one, DO IT. Until then, this looks like the best one out there.
 

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"this set-up did reduce my coolant temp over 8c while @ load (183 KPA) traveling between 50 to 100 mph vs no shroud OE fans off. "

Do your tests scientifically. Don't just say well I drove with one setup at varied speed and I drove another at varied speed. Test them both the same way, both at 55mph, both at 65mph, both at 75mph in separate runs.

"Additionally, if there was high speed flow obstruction by the shroud, regardless of having the fans off or on, the coolant temps should have increased"

How much time did you spend at 50 and how much time did you spend at 100?

"Again, because this was not calculated as it has little to no bearing on whether or not this set-up works. The only pressure differential is the loss of delta p @ the first obstruction (heat exchanger)."

The only reason air will flow through the radiator is with a pressure differential across it. DUH. Don't say this isn't important.

"Not, see my response to your second moot point. "

I think there is a reason that every race car I see has a duct that opens as it goes to the radiator. Go here, they mentioned it on the build-up. http://www.attwilliams.com/

"The duct is an important aerodynamic component. It channels air in from the front of the car and slows it down as it passes through the radiator core. The duct must be designed to slow the air down just the right amount to cause the optimum air volume contraction and therefore create an even air flow to maximize water cooling efficiency." -attwilliams.com

"Actually it's a high volume (cfm), high speed stream of air. That's why I used it for this experiment. A Miata will never see this much air velocity or mass going through the IC, a/c condenser and radiator core. Now, ask yourself, if @ 180 mph I was only getting 10-15 mph air coming out of the back end, how much air really is coming out the back of the radiator core w/ the air speed and cfm one gets by driving. Not much. In my case definitely not enough to cool the coolant while the engine is in load (above 10 inches of vac and above)."

So I did a quick google search that yeilded me these results.

A powerfull leaf blower flows 250CFM

A powerfull carpet drier (like used on dynos) flows 4100cfm

I still can't figure out why you think 'experiment' has anything to do with real life. 180mph air is going to react quite differently then 50mph air when it strikes a stationary surface. Why the air seemed to have such a speed difference is because its spreading out into a wider cone, that high pressure air is trying to spread out everywhere. Pressurize the whole grille opening to a psi equivalent of 180mph air striking a stationary surface then see what the speed difference is.

"Look, what in gods name does aerodynamics have to do with anything that won't see HIGH PRESSURE AIR?"

A restriction is a restriction. This is an aerodynamic device and it is important. I think if you want to really improve cooling you ought to look at ways to decrease the pressure in the engine bay and improve the ducting before the heat exchangers.

You know I just had a thought. I wonder if by restricting (in essence) the surface area of the grille you decrease the amount of air entering the engine bay which decreased its pressure allowing the radiator to become more efficient at higher speeds. This would also explain these results:

"this set-up did reduce my coolant temp over 8c while @ load (183 KPA) traveling between 50 to 100 mph vs no shroud OE fans off. "

This is why im saying you need to do pressure testing, coolant temp is only half the story. It wouldn't surprise me if airflow was limited by the ability of the air to get out of the engine bay.

I think what you have made is a shroud that improves the radiators' high speed efficiency and retains much of its low speed efficiency with fans. Great, but its a band-aid fix.
 
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