Introduction

K&N Filter Conversion

I have gotten lots of questions on the custom K&N filter conversion that I presented some time back. At the time, I did a very superficial mock up of the conversion. Due to the response to that original article and the lack of real development time I put in to the original design, I felt completed to redo my work. Let me also say, up front, that this conversion is not approved by any governmental agencies for use on road. Therefore, state inspections may require that you revert back to your approved air box setup to be legal for on road usage.

K&N makes, what I consider, the best filter elements available today. Since being introduced to them many years ago, I have not run anything else in my performance vehicles. Although, some applications are better than others. My feeling is that the air box on the Cherokee limits air flow, mainly due to the small intake port and its lack of direct fresh air routing. Additionally, the flat K&N filter replacement did not fit that well in my air box. This is odd, in that most K&N factory applications are exact to the micron, but I have heard of this problem before. I don't think its enough of a problem to cause much heartache for most people.

On my first pass, I had used a fairly small cone type filter that had a 3 1/2 inch opening. The stock air tube that runs off of the throttle body to the air box has a 3 inch opening. So, first pass meant that I had to have a reducer, which I made out of standard PVC. This is a problem because PVC is not made for high heat applications. After a while, where the air tube and the filter connected to the adapter I got some melting. Not enough to break down the integrity of the adapter, but enough to notice. So with this in mind, I set out to build a better mouse trap.

I searched the K&N catalog and found a larger cone filter with a 3 inch opening (product #RE0810 ). This would allow the adapter to be a straight tube. This adapter was the major point of redesign. I checked around locally to find out what 3 inch diameter tubing was available. I settled on 3 inch OD stainless steel tubing. This will look better longer than any other metal I could find. It would also make a nice contrast between the black air tube and K&N filter. Any 3 inch OD light metal tubing can be used. The only drawback to the stainless steel is its hardness. Getting holes drilled posed somewhat of a problem, as special (read expensive) bits are needed.

If you look at your air box there are, aside from the main air tube, four other connections. One large 1/2 hose that hooks to the air tube flute and two small vacuum type lines in the back. You will find that one of these vacuum tubes actually runs to the front of the air box to a thermostat. This thermostat controls air flow direction from the main intake or from the heat riser. You will need to relocate the 1/2 line and the other vacuum line. Additionally, there is the air intake side of your PCV system that hooks to the front grommet on the valve cover. This will be relocated completely.

One 11/16 hole needs to be drilled in the center of one side of your adapter, we'll call this the 12 o'clock position. The second hole, 5/16, should be drilled at the 3 or 9 o'clock position. These holes will position the needed fittings so that the 1/2 inch line and vacuum hose connect easily. At this point you will need a 1/2 inch emission elbow fitting and a 3/16 straight fitting. The 1/2 inch emission elbow that I used is actually for a Ford, I found it in the Help section of a local discount auto parts store. Most auto stores now carries the Help line of parts, this fitting is Help #47032. The second 3/16 fitting is a standard vacuum fitting. The 1/2 inch emission fitting has a long and short end, like the one pictured. To fit the emission elbow, you will need to cut off the flanged lip of the long end of the elbow. I got a pack of grommets and sorted through and finally settled on the 3/4 inch one for the 1/2 inch elbow fitting and a 7/16 inch one for the vacuum fitting. You should be able to fit the grommets in there respective holes and then work both fittings in to the grommets. It helps to put a finger behind the grommet when fitting from the outside. I had to tap the cut of end of the 1/2 elbow through with a hammer. If your careful, you can do this without popping the grommet out.

Once the above is accomplished and you have the K&N installed on one end of your adapter, its time to remove the air box. Before installing the adapter you will need to remove the hose off of the PCV intake tube. Replace it will a piece of 5/8 heater hose and run it to a location in your engine compartment that you can tie wrap the end of the hose in a upright position. Then install the K&N breather (part #62-1150). This will serve as your PCV intake. I took this one step further and cut the plastic tube at the vacuum router. I guess this is what the thing is called, its the small multi-tube connector at the front of your intake. Once I cut the tube on the left side of this vacuum router I rotated the grommet and remaining tube and vented on installed my breather by the overflow bottle, as seen in this picture.

A note I wanted to make here about cutting the pipe in the above paragraph. Some may be uneasy about cutting and refitting this connection. In the past year, since I did the original conversion, I have not experienced any trouble from doing this refit. I was never happy with the vacuum router and its hard plastic hoses. This redesign of the K&N setup has gotten me to the point of replacing the whole connector with straight vacuum hoses. I think this will cut down on the hose clutter in the front of the engine if you do it right. Basically, all you need to do this is a long piece of small and large vacuum line. Cut and route the new hose into place and remove the connector once and for all. I also like this because it keeps me from having to spend $25.00 or more on replacing a bad hose.

Now install the adapter into the air tube with the 1/2 inch elbow at the bottom and the 3/16 adapter pointing toward the fender or firewall depending on the curve of your air tube. Reconnect your 5/8 and vacuum tubes, tighten everything down and your ready to go. I did not bolt the unit down mainly due to the restriction of movement that its length affords. I don't think that, unless you plan on jumping your Cherokee frequently, that this will be a problem.

You will notice more engine noise with this open element. Additionally, I have notice a whistle during acceleration, but its not enough to bother me. I'm used to open element intakes and expected some additional noise, if you want yours to stay whisper quiet you should stick with the air box. You may also notice additional fuel fumes from time to time. I normally only notice this when I am in the garage. This too is due to the open element not trapping these fumes where the air box did.

Overall, you should notice marked performance gains and better acceleration. I don't have a dyno to test this on, but I imagine that you are gaining somewhere in the 4-8 hp range, conservatively. And as you can see from the pictures it looks cool too. Performance gains and good looks, what more could you ask for?

Build one for me?

OK, you could ask for that. Will I build and sell you on of these conversion kits? Sure. Total cost for stainless steel adapter, K&N filter #RE0810, K&N breather #62-1150, hose, grommets and fittings for $145.00. For an additional $20, I will include a filter cleaning and oiling kit. This is in line with K&N's filtercharger conversions that are similar in design but are not available for the Cherokee 4.0. The only difference is that they mass produce them and I cant. It may take a few weeks to get the parts and make each one up, but if I get enough request I may start keeping a stock of them.