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.
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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:
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2011-2014:
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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.
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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.
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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