How about one that feeds two three-inch hoses?
  eBay Motors: PAIR OF BUTLERBUILT CLEAR NACA DUCTS
Here's one with an optional transition piece that can be cut to fit a two- or four-inch hose:
Aircraft Spruce: Large NACA Scoop
But note that the inlet is gigantic.
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In theory, there is no difference between Theory and Practice. In practice, there is. - Y. Berra
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