[lunarhighway]

autospeed.com

had quite some articles about air intake modifications.

what i've gathere'd from their testing is that the airfilter is actually just a little portion of all flow restriction in a car, if you really wanted to improve engine eficinty by modding the airflow than youd carefully have to redesign most of the factory ducting.

also factory air filters and airboxes seemed to be pretty good according to autospeed, and in any case these K&R type airfilters should alsways be placed inside the standard or a custom airbox, otherwise you'd just have a potential WAI (wich could be good, but somethinh alltogether different than a free flow filter).

they where also quite enthousiastic about a simple ram intake to the stock airbox, which is you think about it makes a lot of sence, carmakers likely put the intake in a place that somewhat shielded from water, leafes and whatnot, wich could cause problems on an exposed system

so what i gather from all that is that while these pod filters might be perfecly good products (allowing more air trough, being reusable, at the cost of filtering slightly less) there's not magic bolt on device that either delevers more power or improves FE depending on what sells