>Has anyone truly
>believed that they have gotten significant performance enhancement from
>any of the aftermarket filters such as the K&N?
>
>Your comments are appreciated as I will be changing the air filter in my
>1991 Model 535i in the near future.

Well, you asked. I recently installed the K&N replacement filter in my 1994 325is. At the same time, I removed the air funnel thing inside the stock airbox based on previous information that this is also a restriction on airflow.

Observations: More noticeable intake noise, car appeared to breathe better and pull stronger. I noticed significant improvement in driveability with the AC on, car does not seem to bog down as much. Car also does not bog down as much on hard acceleration from a stop.

Testing: As an advocate of the 2nd gear acceleration test, after installation I promptly performed this test fully expecting to register a numerical result reflecting the improvement that my observations were telling me where there-well the numbers showed only a 0.03 sec improvement, after temperature correction. An insignificant improvement.

My opinion: My results show that any improvements in flow are very minor with the standard filter replacement on a 325is. So, I don't necessarily believe this is a performance upgrade that is meaningful. However, I'll never have to replace the filter again!

Regards
Brian Bowden