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1997 Outback, 2016 Forester, 2022 Outback
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Brian, a non-authoritative answer: "Air intake noise reduction". Quite a bit of the structure in the intake plumbing is intended to silence the air intake "roar".
I can't imagine that eliminating that piece of plastic will cause any negative issues, as long as you maintain a good seal in the plumbing between the air filter and the throttle body.
 

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1997 Outback, 2016 Forester, 2022 Outback
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246 Posts
Well, it looks like a "velocity stack", and I suppose that could be its intended function, but having its intake occluded by the filter element would seem counterproductive. Probably some enterprising engineer running intake airflow simulations found a tiny performance boost, and managed to get it incorporated into the airbox design?
Just FWIW, at some point in the early 2000s, Subaru moved the air filter element from a box on the passenger side wheel-well, to the larger box just behind the throttle body. This might be a carry-over from that design transition? There just ain't no way to know, but I can't imagine it making much difference, regardless.
"Velocity Stack" sounds cooler than "Noise Suppression" in any event, and gets my vote :-D.
 
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