Originally Posted by ramicio
Air is being pushed across the blades from an external force.
You could use the same sentence to describe the effect of positive pressure on an exhaust fan. External force(from the greater volume of air being taken in) is pressing against the exhaust fan blades beyond what would be present in a free air environment.
Originally Posted by DuckieHo
Fans in series is actually changing the output. A fan with a modified motor at the same speed is not.
That's why I made that long post earlier questioning whether or not this mod might improve flow under less than ideal pressure circumstances. I think under typical PC airflow conditions this mod may have some benefit, as to how much it is with respect to the cost and change in electrical efficiency I have absolutely no idea. I'm sure the difference is not the best trade off or more fans would be designed with this in mind.