Hi Wayne,
Maybe this'll help:
K&N filter FAQ
What's probably not as obvious is to compare the pressure drop (a way of measuring flow restriction) across the filter vs the carb.
The pressure drop across the carb is needed to help vaporize the gasoline, so you can see some pressure drop even at WOT.
Conversely, you don't want ANY pressure drop across the filter if at all possible since this would reduce engine efficiency. I understand that 1 to 1.5 inches of water is the max pressure drop desirable in an air filter.
A case in point - one of the local Cobra drivers dyno'd his car with and without the air cleaner. On this day, this particular car picked up 40 hp with the air filter removed! Clearly a case of a restrictive air filter - too small for his engine.
If you make it all the way to the bottom of the page you'll probably be the resident expert on air filters
Enjoy,
Tom