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vents
Dr.Alberto Morelli's work in the Pininfarina wind tunnel for the CNR 'banana car',beginning in 1976,probably owns the distinction of the most efficient extractor vent technology I've seen published.
Cooling air off the heat exchanger was divided into four ducted streams which exited the engine bay,blending with the surface flow at exactly the same velocity so as not to trip the flow into turbulence.
If you look for the oil-streaked tunnel photos of the car you will see unperturbed streamlines at these outlet locations.
When the Pontiac Trans Am was undergoing wind tunnel development at the Lockheed Marietta tunnel,the extractor gill slits registered a minor drag increase.
To get a net zero effect or gain may require much tunnel time.Don't know.
If you can snag a July 11,2011 copy of AUTOWEEK,on page 16,there's a small mention of the Iveco 'Glider' tractor-truck with radiator-less flat heat exchangers integrated into the side pods.
Iveco is skipping the cooling system drag altogether.
The Glider also sports photovoltaics on the roof,regenerative braking,beltless engine,and active shutters to maximize exhaust system-generated electricity.
Iveco claims a 40% fuel economy/carbon dioxide improvement for the tractor.
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