[Hauki]

They are really meant for forced induction when they come into their own, for anything less, especially for n/a engines the difference from stock filter is negligible.

Atleast that is in my experience on many n/a cars (& motorcycles) fitting K&N's.

Of course on older cars that didn't have electric trickery, a blocked filter would just make you run rich, this of course is bad, so in this case, a K&N would be perfect (then so would a new stock air filter element).