try running your car without an air filter ;)
the K&N as tested by PF is abysmal as a filter.
been running a k&n for about 50,000km on 2 cars, engines are still running and healthy. its not like most people are driving gravel roads or dirty/dusty enviroments every day.
that test is not a great example of how a filter works either, most cars have a intake system under the bonnet with an air box and resonator etc.