When doing an oil change recently, I put some Mobil 1 5W30 synthetic in along with a K&N oil filter, which appears to be superior to the stock filters. The part number I used was HP-1004 (used for WRXs). I just read that HP-1008 is actually what I needed to use. However, this filter is incredibly small, maybe suitable for a motorcycle not a 2.5L turbo car. Can anyone tell me why such a small filter is the one I should use instead of the WRX one which fits perfectly?