I have heard that K&N and TRD
filters are identical. They are both made from several cotton layers Go to www.knfilters.com.
Great site a lot if useful info is what you find there. I do have the K&N filter installed. Takes only 10 min to replace the stock Air Filter
The engine is now more responsive both in the low and high RPM band. Sound is little more ruffer and deeper. Definitely noticeable. I truly do recommend it. As for the fuel economy, cant tell, have not checked that.
BTW. Take a look at this video I uploaded to the gallery video section. https://www.celicahobby.com/gal3/albums/video/Air_filters.avi
It shows how much AIR different filters let through.
1. No filter. (wach the ball in the plastic pipe)
2. K&N cotton fiter.
3. Foam filter.
4. Paper filter. (stock)
Hope it heples