I picked up where NASA left off with their 'Shoebox' van streamlining and took it to completion.
Starting from their fully-boat-tailed Cd 0.238 van I:
*added body side camber (Buchheim,Deutenbach,and L'u'ckoff)
*added upper edge radii (Hucho)
*added roof camber (Buchheim,Leie,and L'u'ckoff)
*added wheel skirts (Heltemes,Tremulis,Cogotti,Garrone,and Masoero)
*added MOON-esque wheel covers (Shinella,Tsukada,Sakagami,Arai,and Takahara)
*and full wheel fairings (Tamai),allowing 50% of Tamai's factor allowing for wider tires (SWAG).
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We'd have to add back in some features drag associated with a working cooling system,wipers,and mirrors,but that's not a lot of fruit to put back on the tree considering the GM Precept concept car.
PS these are just estimates but should fall close to the tree.