2.5L '91 YJ to 4.0L conversion

I'm relatively new to messing around under the hood and i've never done an engine swap. i know i need to get the ax 15 to go with the 4.0 and trash my ax 5. and i know i need to change the main shaft of the np 231 t-case from a 21 spline to 23.

otherwise i need a complete parts list of what i need for this to work, and if anyone can point me in the right direction, it would be much appreciated.  
'91 YJ, American racing rims, 31" x 10.5"s Interco TrXXus tires, Bestop. rugged ridge fender flares.

It's the x-case input gear that needs to be changed from a 21 spline to a 23 spline, not the main shaft. And that right there costs almost $200. You'd be best off if you find a complete drivetrain, engine, tranny, and x-case all together.

Also, depending on the year of the engine, you'll need the entire engine wiring harness, computer, evap emissions, fuel pump, and the exhaust, including the the head pipe and the cats.

You'll find very inexpensive XJ 4.0L's, but they are not the best to swap into a YJ. None of the XJ accessory brackets are compatible with the YJ engine compartment and you'll have cooling issues because you won't be able to run a big engine driven cooling fan. And don't count on an electric fan to keep things cool. You'll spend at least $350 on an electric cooling fan that will work and another $300-$500 on a good radiator.

Bottom line. It is not cost effective. The cost difference between a 2.5L YJ and a 4.0L YJ is far less than what it will cost you to swap in a 4.0L. And that would not include the hundreds of hours it will take by the time you track down all the parts and get things installed and the bugs worked out.

You'd be much better off creating something you can't just go buy for your money and your efforts. Think V8!  

i would just up and get a YJ with the 4.0L in it, but i already installed new tires, a $600 some dollar sound system and fender flares with a new bestop to keep out the rain. and i need the new engine cuz i'm driving to the other side of the U.S. over two mountain chains and i want something reliable enough to get me there without hassle. the 2.5 won't cut it. i can't even get from south east pennsylvania to the bridge to jersey without over heating and being 10 miles an hour below everyone else.  
'91 YJ, American racing rims, 31" x 10.5"s Interco TrXXus tires, Bestop. rugged ridge fender flares.

drop in a mopar or ford small block!  You could probably buy an entire donor truck with the engine and drivetrain cheaper than a 4.0 swap or yoy could always turbo charge the 2.5  
"WHEN IN DOUBT TACH IT OUT!"

All those goodies you put on the existing TJ can be swapped easily to a 4.0L TJ.  
2001 TJ Sport
- 4.0L I6
- Sport Wheels w/ 30 x 9.50
- Half Steel Doors
- Soft Top
- Daily Driver
- Standard Tranny
- 3:73 Gears