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Props to aerohead for digging up this info:
(quoting him)
"I stumbled onto some tasty little numbers when re-visiting Walter Lays wind tunnel work of 1933.
Lay tested a 'pumpkin seed' model car,which for all intents and purposes IS the 1987 GM Sunraycer,with matching Cd 0.12.
By installing a completely vertical windscreen with square edged header and A-Pillars he doubled the drag to Cd 0.24! Hucho refers to this in his book(s) when mentioning that no amount of boat-tailing will reap benefits if the forebody isn't 'clean'.
What's remarkable about Lay's research,is that by tilting the windscreen back only to 50-degrees from vertical,all the turbulence was killed,and the car was as low-drag as if it had the 'ideal' compound windshield.
Of course,this is only at zero-yaw,and the 'ideal' windshield WOULD have an advantage in a crosswind,but it kinda drives home Hucho's point,that most contemporary automobiles have adequate forebodies,from which to streamline from."
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