Xoutpost.com - Air Filter

Xoutpost.com (https://xoutpost.com/forums.php)

- X5 (E70) Forum (https://xoutpost.com/bmw-sav-forums/x5-e70-forum/)

- - Air Filter (https://xoutpost.com/bmw-sav-forums/x5-e70-forum/78892-air-filter.html)

I have a 2009 BMW x5 48i. Is it ok to change the air filter to a k&n oem fit filter part # 33-2407.

If that is the part K&N specifies for the X5 (and it is) then you can-but really why would you? Regardless of the K&N marketing hype that says you will gain power, you won't-not a bit. Also, nothing filters better than the stock filter. A K&N filter will let larger dirt particles through its filter and into your engine, all for more money and no gain in power.

It's your money, but it would be wasted on a drop-in K&N filter.

Not a big K&N Fan...i prefer stock or foam filters on my vehicles

I wouldn't use a K&N filter either.

Thanx for the info. Were can I get the stock BMW filter?

Wouldn't filter be covered under 48mo/50k miles service by BMW?

Quote:

Originally Posted by X-cellent (Post 799732)

Wouldn't filter be covered under 48mo/50k miles service by BMW?

Yes, but my guess is the dlr won't change it out until ~Insp 1, which may come after warranty/maintenance expires.
I also suspect the OP was thinking that a K&N would 'add 10 hp', 'filter better', etc.

A page full of Threads here on the topic; I would take a Pasadena on the K&N, imo.
GL, mD

Years ago with a BMW K bike, someone did a test to determine the potential of more free-flowing air filters. What they did is simply cover half of the stock filter with plastic or paper, such that the active flow area was half of normal. They then did a dyno test with "half a filter" and normal. There was no HP difference between the two, i.e., the stock filter flowed so well that "clogging" half of it had no impact on HP. With those results, it is difficult to believe a more free-flowing air filter would have any impact on K bike HP.

It would be interesting to see a dyno comparison of an X5 with the stock filter and with no filter whatsoever, to more precisely identify the absolute maximum potential, if any, of reducing air filter resistance to air flow, without making changes in other areas (figuring no filter has the absolute least air flow resistance). I suspect the answer might surprise many people.

P.S. Here is a link to the only independent test of air filters I've come across. It doesn't address HP gains, but does show the trade-off between restriction and efficiency, at least for these particular filters:

ISO 5011 Duramax Air Filter Test Report