There are some very knowledgable people on this forum, Jerry Bransford, Mr Blaine, and several others. What I have learned, both here and elsewhere from having my LJ since 2005 (new) as well as a '83 CJ5 since new, is that the in-line 6 is a very durable motor and does not modify easily for increased performance. You put an exhaust on it (custom or out of the box) and all you will get is an increase in sound, the performance gains will be negligible at best and most assuredly $ per HP will be disappointing, same goes for the "cold air intake" stuff, as well as the "throttle body spacer" and the "tornado" stuff. In reality, the only thing I have seen that dramatically increases HP and torque is to either stroke it (making it somewhere around a 4.6 liter) or put a super charger or turbo charger on it. None of these three are inexpensive, but all three give significant boosts in HP and torque. My suggestion is to save your money for one of those or increase the capabilities through suspension, lockers, winch, etc. It is, after all, a JEEP, not a hot rod....... YMMV, just MHO