I searched for this for a while, but was unsuccessful in finding any info. Don't shun me if I have missed something. What kind of gains can I expect with a Perrin Panel Filter over the stock filter, with the snorkle already removed and MBC set to 15 PSI on an 04 WRX sedan?

 

not too much at all. in fact hardly any. the panel filter is just re-usable and you may claim a gain on the butt dyno. Other than that you get a bit better airflow over stock. I used to have a K&N but went back to the OEM paper filter because i was scared of oil getting on the sensor. I couldn't tell a real difference.

 

The main reason I got it is for cleaner air. I also would hope that at times more air would be able to be pulled through it when needed, but who knows.

 

It will help you save money on filters in the long run... the very long run. That's about it.

jason

 

Yeah, by my calculations, assuming a 1000000 mile life on the aftermarket filter, it would save you aproximately 33 OEM filters, assuming you would change the stock filter every 30000 miles. Over the 1000000 mile life that would save you $1000. Hhmmm, that's not really that much. Now, in a more practical example, the aftermarket filter would save us roughly $30. Interesting.

 

If you get a Perrin Filter, I recommend buying two so that you don't have to wait for cleaning the filter and you can let it soak a day or two in soap and just swap them.

The benefit of a foam filter is mainly due to the fact that they can "pack-up" with alot of material and still maintain good flow. A paper filter is a continuous membrane with little depth versus the porous nature of foam.

 

Plus it's yellow!

 

And we all know yellow flows the fastest.

 

And yellow stickers add the most hp!

 

Buying two filters gets to be a little pricey although it might be worth the convenience to some.

As for the factory paper filter, it has a large number of pleats that increases the filtering surface area greatly, without taking up much more room. By their very construction, neither foam nor gauze-and-mesh (K&N) can have as much surface filtering area, although square inch to square inch they filter more efficiently.

Vishnu Performance claims that they do not include K&N drop-in panel filters in their WRX kits because the filters lost 2 to 3 horsepower compared with a new factory paper element. While this may be true, the K&N may filter consistently better over a longer period of time while the paper element will probably become clogged and restricted over the same time period. I think the paper elements need to be changed more often than the 30k miles specified in the Subaru maintenance schedule.

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"…axles of evil…" - george w. bush

 

Foam panel filters are a matter of reusability, like most everyone said. I've also heard that they make the WRX more "drivable" in a sense that the boost threshold is lowered by a bit; that is, the turbo spools a bit quicker. That's about all. So why not, right?