I'd be more worried about the fundamentals...
filtering of air with the filter hanging directly in the duct?
how well do pod filters really work?
i personally wouldn't want to risk my motor by ingesting more particles that strictly necessary... plus by 'boxing' up the duct, how is it any more effective than boxing up the filter in the engine bay?
plus, if you're sitting in traffic, the 'hot' engine air would be so quickly purged with a ducted box in the engine bay anyway.
you might make 2kw more.