Changed my engine air filters last night, took the old mann ones out and popped in new stp filter in the same direction. Today I was cleaning up and picked up the old fillters to throw in the trash. I notice the clean engine side of the filter pleats while under vacuum would collaspe the pleats against each other reducing surface area and airflow instead of expanding pleats to promote airflow. The Mann filter had a perpendicular support ribs to HELP prevent this, but I didn't check the STP fillter for the ribs. Also the pleats partially block intake airflow on the dirty side. Is this how needswings cai intake improves airflows? I am thinking a couple of adapted mass produced air filter housings from the salvage may be better.under the grille, may rival the needswings system. PITA to change. Would require sealing/clamping existing cai intake tubes. Sorry I no longer will ever do the foam or k&n style filter systems.

 

You are applying airflow and air pressure to the filter backasswards. In practice there is more pressure (ambient) on the outer face than the inner face.

 

covers come in 2 shapes of cavities, so depending on that, is the kind of filter you have to buy.
1 of them is same thickness, the other has a step, so half is higher than the other.
so 1st you need to open the cover and find out the shape: if same thickness, or with step.
if you try to press the wrong 1 in place you may let the air flow straight through the duct without getting filtered.
or you smash the filter badly and same thing happens.
then, you need to find an add that shows clearly that shape..
and some adds dont specify if the price is for 1 or 2-and you need 2.
sometimes the illustrations show 2 but when you get the package you get 1.
so be careful.