K&N Filter

 experimented in the past with a smaller air filter as seen in the tips section.  It helped the acceleration and top end a bit but the problem was the filter was so small it got dirty really fast.  Dust is prevalent on most AZ trails and a stock air filter can be ready for a change after only 3 to 4 runs.  I had seen this mod done and finally got around to ordering a filter.  One word of advice, if you order from Summit Racing, do not go by their web page.  The first filter I ordered had the inner diameter of the mounting flange listed wrong.  I called and talked to a sales rep and discovered they carry a lot more sizes not even listed (unless you directly enter the part number).

Parts

KNN-RE-0930 - Summit Racing $41.39

41221 - Napa 3" Dia Exhaust Elbow $22.59

or 

RV sewer hose elbow - from Walmart, about $2

(Thanks to Larry Robertson for that tip)

The exhaust elbow was really expensive, if anyone finds a better source let me know.  Pep Boys and Checker only went up to 2.5" dia.  As you can see the 3" dia elbow (yellow) fits perfectly in the stock air filter hose after you remove the stock air cleaner box.   The K&N is a 6" long model, they have 4", 4", 7", and 9" available as well in the 3" dia mounting flange.

To secure the filter I used some steel strap with holes in it to wrap around the filter flange and bolted it to one of the stock air box mounts.  You could also weld a bracket to the elbow and bolt that down as well, just remember to use a rubber grommet to allow some movement. 

To take care of the vent tube for the valve cover I got a little $9.99 filter at Pep Boys (sorry, lost the part number).  To attach it I picked up a 1/2" pipe fitting from their hardware section. Some people are going to look at the price and see you can buy a complete setup for a couple dollars more from some of the Samurai vendors.  The advantage to this setup is a much larger filter, you'll be able to go longer between cleanings.