[JulianEdgar]

Originally Posted by aerohead

1) I don't know that within the context with which you imply.
2) A 'Kamm-back' based fastback, of any length, would already have the smallest wake, highest base pressure, lowest lift, and lowest drag. A spoiler wouldn't alter that situation. A spoiler could add 'direct downforce,' however, historically, would come at the expense of higher drag, or danger to pedestrians if not thoughtfully conceived.

I am talking about modifying real cars, not theorising about shapes. A rear spoiler on a fastback shape can reduce drag and lift: refer to Page 304, Aerodynamics of Road Vehicles, 5th edition.