air dams vs ducts

[advo@mn.rr.com]

Many Studes thru the years have ducted air from the area in front of 
the third member to the low pressure area behind the rear window.  My 
question is whether an air dam at the front of the car creates enough 
low pressure under the car that air flow thru a rear deck duct would be 
in the wrong direction. Would one cancel the other out? Who would win 
at 150 mph.....
Greg
Salt2Salt.com