Both are somewhat the same in performance, just different designs. Try doing a search on the issue because it's been beatin' to a pulp. No worries though, to summarize it for you some guy reasearched it very well and found that the OEM paper filtered the best, however, the K&N, Perrin etc etc allowed better airflow at the cost of "less-clean" air when compared to the OEM paper filter. Overall, it's not a big issue...what gets past the K&N, Perrin, green filters isn't going to hurt anything.

The other conclusion is in regard to the filter oil screwing up the maf sensor. I never had a problem with this when i used a K&N. just be sure that when to go to clean it and re-oil it to let it sit out for about 2 days to be sure the oil has soaked in. Then wipe off any excess and presto...meanwhile use the old oem paper filter while the other's drying.

I on the other hand switched back to the OEM paper element because it seems to clean a bit better and they last a good while.


eric

 

the fitment issues i've heard about is just because the drop in filter seems ot be a tad bit bigger, which can be easily adjusted. IMO k&n have a much better reputation in filters and that's what i would go with.

 

After conducting months of exhaustive research, I'll tell you this: Green Filters are the best drop-ins money can buy. There's a few threads here on them, run a search. Perrin is superior (surprisingly) than K&N for the WRX; the K&N is essentially equivalent to the stocker except for the fact that it can be reused. The Green makes for the best performance and durability of the three, and Peaty swears on it.
Oh, and don't forget the silencer removal while you're at it

 

Green filter info

 

i have the perrin on my car and it runs just fine, didnt notice any sort of loss (or gain for that matter) compared to the stock. the nice thing about the perrin (like the k&n) is its reusable.

i have also ran the k&n filter for a short period as well and didn't really notice any sort of difference.

my conclusion is its really up to you on what way you want to go, neither is going to be significantly better imo.

 

K&N. I would also check out the TurboXS shorty intake at fastwrx.com. Its not too pricey:

"This simple and inexpensive intake from TurboXS features a factory-sized bore for the mass air sensor, to ensure accurate measurement of the incoming air. (Some other intakes mess up the mass air reading, which can lead to dangerous air/fuel ratios). It eliminates the factory airbox, freeing up space for front-mounted intercooler piping.

Includes CNC-machined mass air pipe, mounting bracket, and a lifetime genuine K&N filter."


http://www.fastwrx.com/turshorin1.html

 

Exactly.

I have a Perrin filter, and i like it. Instead of cleaning it, I just buy a new one from MPJPERFORMANCE every year... (I'm just tooo lazy!)

-Gagan

 

I have K&N but haven't tried the perrin yet..So for now i'll reserve my suggestion until i try one(perrin)