Those station wagon deflectors redirect a jet of air across the window, but that doesn't magically snip off the wake. The current thinking is Faschenfeld tearing edges (newer Prius) or vortex generators.
Car or van? That's a broad category. It's easier to go from 0.40 to 0.30 than from 0.30 to 020. IOW starting condition can vary.
You want a guaranteed improvement? Chop the top.
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.Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster
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.You can't be wise and in love at the same time. -- Bob Dylan
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