One thing I never liked about my TiiCo was the air filter. The way it fit in its can left very little room for air to actually get into and through the filter. I decided to solve the issue by replacing the paper filter with a K&N® air filter. The K&N® filter has two major advantages over the "stock" filter. 

1. It can be cleaned and reused, instead of needing to be replaced.

2. Just by its very nature, it breathes better than the stock filter.

In my application, I was able to get even better airflow because of the filter I chose. Instead of going with a direct cylindrical replacement, I chose a truncated cone shape. Because it's cone shaped instead of cylindrical, it had more clearance between it and the wall of the enclosure so more air could get to the filter. Another thing which let the new filter breathe better was the fact that the end of it also had filter element to allow air to go straight into it instead of having to go around to the side of the filter.

The K&N® wasn't a direct fit, though. I did have to modify the filter slightly. the "flange" at the bottom of the filter was a little too small to fit over the neck of the stock filter mount. I solved this problem by cutting off the flange and widening the hole on the bottom of the filter so it would go over the neck of the filter mount. A word of warning, however. Don't remove too much material from the bottom of the filter because you still want it to be a tight fit on the neck of the mount.

This shows the side by side comparison of the filters.

This shows the "end on" comparison of the filters.

This shows what I removed from the K&N to make it fit in place of the stock filter.