Review on K&N High Performance Universal Clamp-On Air Filter: Premium, Engine Replacement Filter - 2.75 In Flange Diameter, 4.5 In Filter Height, 1 In Flange Length, Round Tapered Shape (RG-1003RD-L) by Mike Meyers

This is a very small capsule filter - good if you don't have a lot of room to squeeze it in. I really like that as size really doesn't matter in terms of airflow. A major downside for me is that it has something of a "universal" filter neck. They give you a set of rubber stacking adapters to give you the right size. In the end I was only able to "approximate" my piping size and had to stretch it a bit. This is a problem solver. If you are replacing a regular size filter, purchase a pre-assembled unit. Only buy it if you have non-standard diameter pipe that you need to work with.