Is there a noticeable performance difference with these air filters? Is it worth the extra money plus periodic cleaning and applications of a "special oil" lubricant?

If you have a Honda S2000 that regularly sees 9000 rpms you might notice a performance difference. However, on most cars driven under typical conditions the difference will probably only be in sound of the intake, if any. The main benefit to the K&N filter under typical applications is the longevity of the filter. It likely will pay for itself over the life of the car, but you need to be very careful to not over oil it after cleaning. If you over oil it, the excess oil can easily accumulate on the MAF sensor and cause fuel economy concerns. Most folks agree that the airflow benefit happens only at very high rpms, ranges in excess of typical urban driving.

-Rod

I have used many K&N's over the years. Often they do not have much benefit over a good quality, reasonably clean paper filter.

Their greatest advantage is with custom intake set-ups. They have a wide variery of shapes and sizes that can fit just about any custom intake set-up, including compact ones for where space is at a premium.

Their greatest disadvantage is they are not very good at filtering air, regardless of their advertising.

I have placed a thin film of oil or grease on the side of the air filter housing, where the air should be clean. With a stock paper filter, the grease stays clean. With a properly-oiled K&N, the grease gets dirty and gritty, over time, from dirt that is sneaking past the K&N.

It completely depends on the vehicle. Some stock intakes are remarkably restrictive, others are more than adequate. One thing that does tend to happen with the oiled cotton filters is that they sacrifice filtering for flow. They tend to let more particles through, especially as they get dirtier.

The latest technology has filters that don't use oil impregnation to trap dirt. They flow as much as a K&N, but filter much better. AFE is one company that has dry filters that flow a lot but don't need oil.

I used a cone filter from K&N the RE-9020 along with a 90 degree elbow and some 3.5 inch piping to make my CAI. These are the things that I noticed better throttle response, car felt more energetic, sounded like it was revived much better than with the muted sound it had with the stock air box.

But the filter does get dirty after time and oil on the MAF could lose you mpg so I check that out and clean it but half the time it’s not even dirty. I cleaned my filter at 100k now im at 108k so I might clean it again, but I’ll see what K&N recommends on the schedule cleaning of their filters. In the mean time ill take what I learned from here and see if it applies to my dirty looking filter.