This issue has been around since the Earth cooled.
K&N did not develop the FIPK for the ZJ 4.0L due to lack of improvement on the dyno.
Myself and many others have cobbed one together using the stock air tube and a conical K&N, or other. The heatshield from the 5.2's will bolt into the 4.0 ZJ's, but they are hard to find, and I do not know of anyone that has ordered one from K&N, or if they are even available as single units.
The K&N drop in filter is much improved over the stock paper design. For even better flow, many have removed the restrictive airbox intake that goes to the radiator area somewhere.
I'm currently working on a snorkle/cold air intake, using a snorkle from a Toyata Hilux (3.0L diesel). Stay tuned for those results.
A forum community dedicated to Jeep Grand Cherokee owners and enthusiasts. Come join the North American Grand Cherokee Association and participate in discussions about performance, modifications, classifieds, off roading, trail reports, troubleshooting, maintenance, and more!