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2005 Outback 2.5i
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Discussion Starter · #1 ·
I can't believe I never noticed it before but, I just cleaned my k&n and saw another filter, post filter. I mean practically touching each other. Is this filter necessary? If it is, is it something the dealer has to order? I just would like to cut down on the air resistance as much as possible, otherwise what is the purpose of even having the k&n?

'05 outback 2.5
 

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I believe that's added in the California and PZEV emission spec models. It's a charcoal type filter. Most likely dealer-only part, although with the greater number of PZEV's out there now, there might be some aftermarket suppliers.

See: http://opposedforces.com/parts/lega...arger/air_cleaner_and_element/illustration_2/

For what it's worth, my sense of posts here is that using the K&N or similar filters is of marginal benefit at best. I wouldn't worry about air resistance. The car is designed to work with the factory filters (when properly maintained).
 

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Discussion Starter · #3 ·
So it's just best to leave it in? My iPhone didn't translate the code in your link.
If anyone else has an opinion, I'm still curious. Also, my OB doesn't say anything about being a PZEV, but that doesn't mean it's not.
Thanks!
 

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my OB doesn't say anything about being a PZEV,
There were PZEVs built going back some years, but it's only more recently that they've been promoted and marked (tags on the rear gate) as such. Look at the emissions label on the underside of the hood -- it will indicate the level of emissions control the car was designed/assembled to meet.

The PZEV level is achieved, in part, by "tweaking" rather than a whole different design. For example, the charcoal filter is added behind the main air filter to prevent any remaining gas fumes in the intake manifold from escaping out to the atmosphere when the engine is turned off. Instead, the fumes will be trapped by the charcoal and then drawn back and burned when the engine is restarted. (It's essentially the same function as the charcoal canister associated with the fuel tank evaporative emissions control system.)

Here's a similar thread: http://www.subaruoutback.org/forums/66-problems-maintenance/35224-filter-mesh-behind-air-filter.html
 
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