So I've had in the FAQ for a while, and its mentioned in various places that the WJ intake is worth some horsepower on the older motors. This intake was found on 99-up WJs. Below is the standard "old" style YJ/XJ/TJ intake compared to the WJ intake. Pretty evident why it's worth some power.
After doing this swap, pretty much blindly because there weren't any writeups I could find, I figured I'd do a writeup. It will go onto the older style 4.0s with some minor modifications.
The largest hurdle is the mounting of the power steering pump bracket. The WJ (and newer style 4.0s) use a different mounting pattern and depth than the older 4.0s. First you need to bolt the bracket to the bottom hole in the water pump (Just like factory). Then make two small brackets to reloace the pump. If you notice in the picture below all I have is two pieces of flat plate with small bends in them with two holes drilled in them.
Now because the powersteering pump will be relocated the belt ends up needed re-routed. Notice the missing bolt in the image below. Its the top bolt in the belt adjustment, the lower bolt and the one that goes in from the bottom is still there. I tried using a bolt that ground the head down, but the belt must have just barely hit it on day 2 and it shredded the belt, so I took it out to eliminate the chance of this happening (To be fair I forgot to tighten down the power steering pump, so it could have moved. I just chose to eliminate all possible chances of another belt being destroyed). There are still several bolts holding everything together, in my opinion it wasn't necessary to have that bolt.
Next because of the change of the location of the power steering pump and the angle it's not at you will lose most of your adjustment. The pump will still move the full amount of travel, but due to the angle it's not adjust much by moving it. So the belt must be almost exactly the correct size. This is what I found the best routing option for the belt to be after relocationg the power steering pump.
This routing unfortunately places three smooth pulleys in a row, and requires the grooved side of the belt to ride on a smooth pulley. If you use the factory pulleys I found 744K6 belt worked perfectly. However I chose to switch to a grooved pulley for the top idler to help keep the belt located, and so the grooved side of the belt wasn't riding on a smooth pulley. I used Gates idler pully 36320. This will bolt right on using the factory bolt and bushing, I did however need a single 3/8" washer to space the pulley out. This pulley is slightly smaller though, which meant I had to switch to a 735K6 belt. The Gates pulley will be metal, other manufacturers may be plastic.
The Gates pulley at the top there. Notice it's a 7-rib pulley, but works perfect.
As for the final part of the install, almost everything will swap over. Since I needed a return line I had to use my factory YJ fuel rail. The throttle body is the same on the WJ and YJ except for a few minor differences. The WJ one does have a vacuum port on it. You can use either. You can also interchange the IAC and TPS sensors, so you can transfer over your YJ sensors to use the factory plugs. The IAT can also be relocated to a back port so your factory wiring will reach. Other than that I just plugged off the additional ports, as most were not used in my application.
This intake will work either both new and old style exhausts. It will work fine with the early 4.0 intake gaskets as well.