Reasons for less power with K&N:
1. too much oil (but this will fix itself eventually, the excess will be drawn into the port)
2. too small (diameter X height)
3. the top is too close to the air horn
The CFM flow per inch of filter area is excellent.
If your filter has cloth or paper in it, don't use oil unless it says so.
Metal mesh is always oiled if it's the only material used, some are designed to hold a thin layer on the bottom surface. I prefer single grade heavy oil, lighter stuff has a tendency to pass through the engine too quickly.
