Originally Posted by Penguin

If a K&N filter is oiled improperly (and some say even if oiled properly), it can mess-up the MAF sensor by depositing a thin film of oil on it. So under-oil it and it doesn't filter well, over-oil it and it will likely mess-up your MAF. You've got to get it "just right."

Frankly, if BMW though less air filter restriction would help performance they could have easily used a larger, less-restrictive paper filter to accomplish that end.

They did not.

Now, this is not directly related to the BMW auto engines, but...


K&N makes a filter for older BMW K bikes, making similar claims. A couple of guys put a K bike on a dyno and tested it three ways (a) stock paper filter, (b) stock paper filter with half of the filter blocked off, and (c) K&N filter.

Results?

Same HP for all three.


I don't think BMW engineers design their engines so that the air filter is the breathing bottleneck.

Now, if you start modifying the total airflow system, with things such as exhaust, intake manifold, etc., the air filter might become a limiting factor.

But I doubt that a simple air filter change to a K&N will do anything other than (a) take money out of your pocket, (b) increase maintenance, and (c) potentially mess-up your MAF.

Of course, that's only my opinion, and I an sure K&N and some others will disagree.