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Blocking off portions of the front grill for improved downforce and reduced drag

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Usually blocking off the airflow to the grill is bad for cooling and good for reducing drag at high speeds.. however, if you already have hood venting (something like a Tiger hood or louvered hood) it seems you can gain downforce by blocking off parts of the hood to airflow.

Has anyone tried this? did the pro races from the old days use this in the world challenge S197s?

Edit, got this pic from trackaeroconsulting.com shows quite a bit of the front grill is blocked.. Here is the paper on it https://racelouvers.com/content/Race-Louvers-Mustang-Hood-Shootout-Wind-Tunnel-Data.pdf it essentially says block as much radiator opening as you can while still maintaining cooling. this not only reduces drag but also increases front downforce.

rack-aero-consulting-grill-screens-and-restrictors.jpg
 
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That Gt4 has been in a wind tunnel, and specifically designed aero package
( most of which we left in the bus stop at Daytona) So it's an overall package. In the S197 grand am/ pwc days, we didn't block much off in the grill. The grand am car did some tunnel testing, BTW.IMG_0474.jpg
 
29
25
Exp. Type
HPDE
Exp. Level
Under 3 Years
SE Virginia
Usually blocking off the airflow to the grill is bad for cooling and good for reducing drag at high speeds.. however, if you already have hood venting (something like a Tiger hood or louvered hood) it seems you can gain downforce by blocking off parts of the hood to airflow.

Has anyone tried this? did the pro racers from the old days use this in the world challenge S197s?

Edit, got this pic from trackaeroconsulting.com shows quite a bit of the front grill is blocked.
In a way, Ford tried this when they shrank the GT350s grill opening for the 2019 model year.
I'd be curious to see how many square inches of opening they left on that grill.
The pic you posted could just be a stock 2019 grill.
 
The pic you posted could just be a stock 2019 grill.
The example picture looks like FR3Z-8200-BA to me. FR3Z-8200-AB was a slight bit more open, matching what you mentioned earlier regarding the change.
Vorshlag ran their 2011 with a completely closed off front grille, to which I'm sure you can read Terry Fair's reasoning in detail in the development thread on his site.
1684864569251.png
It's maybe a technical distinction, but decreasing the frontal openings doesn't increase downforce so much as reduce lift. In the stock configuration, the air entering the front of the car after doing its duty in the heat exchanger is designed to duct out the bottom of the engine bay. In 2011, Ford advertised a 6% aero benefit over the 2010 body design. But wait, the body was the same between 2010 and 2011, right? In 2011, they increased how far down the rubber lip extends on the 'lower stone deflector' BR3Z-17626-B compared to 2010's part number AR3Z-17626-A.
2010:
1684868055423.png
2011-2014:
1684868037591.png
The effect is two-fold, 1. Keep more air out from underneath the vehicle by bringing down a lip that forces it to the sides and 2. Act as a larger wicker to further enhance the low pressure zone AHEAD of the slatted engine tray openings where a portion of the heat exchanger air is encouraged to depart.
1684868206309.png

If everything stays the same and someone removed the lower engine wicker, they'll get worse aero for those two reasons. If they introduce more air into the engine bay in the stock configuration, let's say by opening up the grille opening or removing the grille entirely, more air will be forced to exit out the bottom of the vehicle. This may increase air mass across their heat exchangers (if it actually enters through), but will also generate more drag and lift since more air is slamming into the firewall (parachute) and exiting out the bottom of the vehicle. If they were to re-route and have the air exit out the hood, it becomes more of a question of how well they're controlling the air and it can run the gamut between just adding louvers and it still hitting the firewall to creating a fully-ducted and sealed pathway. Another pro to a small frontal opening is when high pressure air comes in via a small opening and then expands to fill a larger volume (well-ducted heat exchanger with a surface area larger than the opening), the air slows down and is allowed more time to interface with the heat exchanger's fins therefore becoming more efficient. That's why on a lot of professional fully-ducted systems you'll see a small opening flare out to a larger heat exchanger volume and then neck back down again before exiting the hood.
1684869247754.png

So yes, you want to limit your air openings just to meet your cooling needs, but there are other factors at play that influence that decision making process:
How well is the incoming air ducted? If there's a significant amount of bleed passageways, you may not even have an increased air mass enter your heat exchanger in the first place.
What are the environmental conditions? If a normal track outing sees temperatures of 100F+, you may be forced to open up more airways compared to someone living in the North just due to the efficiency of the ambient air.
How fast is the track? If you're going to a track that's slower, you'll have less penalties for opening up more frontal air area.

This is just me blabbering and I'm not an expert so feel free to ignore it compared to members who may know more :)
 
Last edited:
29
25
Exp. Type
HPDE
Exp. Level
Under 3 Years
SE Virginia
^ Pretty much that.

(With the exception that those part numbers are for a Mustang GT grill, and the example picture from the OP is a GT350.)

Also, slowing down the air as it passes over the heat exchanger is not just good for cooling, but as a bonus it reduces drag. Using a "nozzle" shape to accelerate the air again produces some thrust and offsets more drag.
(You can't get a net thrust this way, but maybe offset 40% of the drag from the radiator IIRC.)
The manufacturer talked a lot about that, back when the Mustang had an SOHC V12. 😁

P-51 Mustang, radiator diagram.jpg
 
In a way, Ford tried this when they shrank the GT350s grill opening for the 2019 model year.
I'd be curious to see how many square inches of opening they left on that grill.
The pic you posted could just be a stock 2019 grill.
In 2019 they simply gave every car the GT350R grill opening. I'd love to believe that they did this purely for aero efficiencies, but something also tells me that simplifying that piece to a single part number as opposed to two part numbers offered them some costs savings as well. It's up for debate whether the aero engineers or the bean counters were leading that decision, but I know which camp I'm leaning towards.
 
That Gt4 has been in a wind tunnel, and specifically designed aero package
( most of which we left in the bus stop at Daytona) So it's an overall package. In the S197 grand am/ pwc days, we didn't block much off in the grill. The grand am car did some tunnel testing, BTW.View attachment 86364
That Phoenix car is gorgeous, its always been like a holy grail for me of S197 race machines... I have an aftermarket wide open grill on there now, way too wide open.. it flows so much more than the original one that my tiger hood would rattle at 80mph. i'm gonna work with the Track Aero guys as they have great prices and back it up with wind tunnel results. Have you heard of them?
 
The example picture looks like FR3Z-8200-BA to me. FR3Z-8200-AB was a slight bit more open, matching what you mentioned earlier regarding the change.
Vorshlag ran their 2011 with a completely closed off front grille, to which I'm sure you can read Terry Fair's reasoning in detail in the development thread on his site.
View attachment 86384
It's maybe a technical distinction, but decreasing the frontal openings doesn't increase downforce so much as reduce lift. In the stock configuration, the air entering the front of the car after doing its duty in the heat exchanger is designed to duct out the bottom of the engine bay. In 2011, Ford advertised a 6% aero benefit over the 2010 body design. But wait, the body was the same between 2010 and 2011, right? In 2011, they increased how far down the rubber lip extends on the 'lower stone deflector' BR3Z-17626-B compared to 2010's part number AR3Z-17626-A.
2010:
View attachment 86392
2011-2014:
View attachment 86391
The effect is two-fold, 1. Keep more air out from underneath the vehicle by bringing down a lip that forces it to the sides and 2. Act as a larger wicker to further enhance the low pressure zone AHEAD of the slatted engine tray openings where a portion of the heat exchanger air is encouraged to depart.
View attachment 86393

If everything stays the same and someone removed the lower engine wicker, they'll get worse aero for those two reasons. If they introduce more air into the engine bay in the stock configuration, let's say by opening up the grille opening or removing the grille entirely, more air will be forced to exit out the bottom of the vehicle. This may increase air mass across their heat exchangers (if it actually enters through), but will also generate more drag and lift since more air is slamming into the firewall (parachute) and exiting out the bottom of the vehicle. If they were to re-route and have the air exit out the hood, it becomes more of a question of how well they're controlling the air and it can run the gamut between just adding louvers and it still hitting the firewall to creating a fully-ducted and sealed pathway. Another pro to a small frontal opening is when high pressure air comes in via a small opening and then expands to fill a larger volume (well-ducted heat exchanger with a surface area larger than the opening), the air slows down and is allowed more time to interface with the heat exchanger's fins therefore becoming more efficient. That's why on a lot of professional fully-ducted systems you'll see a small opening flare out to a larger heat exchanger volume and then neck back down again before exiting the hood.
View attachment 86394

So yes, you want to limit your air openings just to meet your cooling needs, but there are other factors at play that influence that decision making process:
How well is the incoming air ducted? If there's a significant amount of bleed passageways, you may not even have an increased air mass enter your heat exchanger in the first place.
What are the environmental conditions? If a normal track outing sees temperatures of 100F+, you may be forced to open up more airways compared to someone living in the North just due to the efficiency of the ambient air.
How fast is the track? If you're going to a track that's slower, you'll have less penalties for opening up more frontal air area.

This is just me blabbering and I'm not an expert so feel free to ignore it compared to members who may know more :)
Excellent post mwjscn!! i agree on all fronts and nice work pulling the 2010 vs 2011 part numbers up.. i have an ingot silver 2012 much like yours with the Brembo kit. years ago i added the boss 302 front 'splitter' if you want to call it that, i dont know if that is better than stock 2011/2012 GT. after speaking more with Albert Watson over at Race Louvers he said since my car is 100% stock aero the best improvements would be the big center Louver designed to fit the cobra jet intake and the two side hood smaller ones slightly more rearward. Then tape off the grill as much as possible but maintaining cooling.. I run at Waterford and since this beast runs on E85 it never even gets warm! i have that huge Setrab oil cooler kit i'm sure you have seen around. at the moment i'm on old Pilot super sports 275/40/18 and the Vorschlag 18 inch China made flow form wheels. i can leave it in 3rd the whole time with all stability stuff turned off. stupid car is already fast!! i need more safety kit.
 
^ Pretty much that.

(With the exception that those part numbers are for a Mustang GT grill, and the example picture from the OP is a GT350.)

Also, slowing down the air as it passes over the heat exchanger is not just good for cooling, but as a bonus it reduces drag. Using a "nozzle" shape to accelerate the air again produces some thrust and offsets more drag.
(You can't get a net thrust this way, but maybe offset 40% of the drag from the radiator IIRC.)
The manufacturer talked a lot about that, back when the Mustang had an SOHC V12. 😁

View attachment 86428
Hey i watch Greg's airplanes channel on youtube he talked all about this free acceleration and cooling effect. I get it now!
 
6,576
8,576
That Phoenix car is gorgeous, its always been like a holy grail for me of S197 race machines... I have an aftermarket wide open grill on there now, way too wide open.. it flows so much more than the original one that my tiger hood would rattle at 80mph. i'm gonna work with the Track Aero guys as they have great prices and back it up with wind tunnel results. Have you heard of them?
I have, but other than that, I'm not nuch familiar with them, My world these days orbits around FIA "spec" production cars, so everything is already engineered into the car. I miss the good old days in Grand Am and PWC when you could build your own stuff. I think the zoomy factory types got tired of being beat by a 4 year old Mustang built from a salvage title.
PWC basically legislated that car our of existence when AJ won the first 2 races with it. The video is posted on here someplace.
 
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29
25
Exp. Type
HPDE
Exp. Level
Under 3 Years
SE Virginia
In 2019 they simply gave every car the GT350R grill opening. I'd love to believe that they did this purely for aero efficiencies, but something also tells me that simplifying that piece to a single part number as opposed to two part numbers offered them some costs savings as well. It's up for debate whether the aero engineers or the bean counters were leading that decision, but I know which camp I'm leaning towards.
I wish they had done that for 2020. I have a 2020 GT and the upper grill is almost entirely open.
 
Stupid question, i have a big carbon bladed grill on my s197 if i tape it at the back its gonna be easier.. does it matter if i tape the front or back surface? i'm guessing probably you need to tape the outside surface..


mygrill.jpg
 
50
42
Exp. Type
HPDE
Exp. Level
3-5 Years
California
Stupid question, i have a big carbon bladed grill on my s197 if i tape it at the back its gonna be easier.. does it matter if i tape the front or back surface? i'm guessing probably you need to tape the outside surface..


View attachment 86593
It would be more efficient to block it off from the front, but I think the efficiency difference will be very minimal. I would personally block off the back because it will be easier and it will look cleaner.
 
29
25
Exp. Type
HPDE
Exp. Level
Under 3 Years
SE Virginia
Stupid question, i have a big carbon bladed grill on my s197 if i tape it at the back its gonna be easier.. does it matter if i tape the front or back surface? i'm guessing probably you need to tape the outside surface..


View attachment 86593
When you talk about taping from the front, do you mean like this? 😇
GT500 taped for Standing Mile race.png
This is what somebody did with their S197 for "standing mile" racing.
This is probably the most streamlined S197 I've ever seen.
 
29
25
Exp. Type
HPDE
Exp. Level
Under 3 Years
SE Virginia
That radiator fan had to have been working overtime lol
Maybe on the cool-down. They must have known in advance that at 200mph they'd be getting enough air through the strip they left open at the bottom.
Once they accomplished their 212mph run, maybe they ripped the tape off as fast as they could. 🤷‍♂️
 
98
131
Exp. Type
HPDE
Exp. Level
20+ Years
Charlotte
I just added Race Louvers to my 2019 GT350. No mods to the factory radiator enclosure. I’m going to run Road Atlanta late June and see how it does. Not that excited about removing the front of the car to box in the radiator….

What can I realistically expect in terms of lift reduction and potential cooling benefit?
 

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