[Piwoslaw]

Originally Posted by tasdrouille

It all comes down to filtration and flow. This study proved that K&N flows better. Yes, by a huge 2 inches of water at 350 CFM. That sure is good enough for a 10% in fuel economy. It also does not filter very well.

NO air filter at all has even better flow and even worse filtering (and costs less than K&N), but will it increase FE by as much as 10%? Maybe if you add to it LRR tires and an alternator kill switch, then maybe so. That reminds me of an advert spoof in MAD magazine:
Play-C-Bow health pills - When taken with a glass of water they help hydrate your body. They help increase muscle mass when taken before or after intense weight lifting training. Etc.

The best way to increase flow through a filter, without increasing the amoung of dirt that makes it through, is to increase the filter's area. Just adding a second OEM filter and intakes, parallel to the original, would give better flow (and cost about the same) than most super aftermarket stuff. But how much will it help? I thought about doing just this, but after talking to a few car mechanics it turned out that I'd spend time and/or money on something that wouldn't make a noticeable difference, especially at the rpm range I stay in.