I've been looking for a TJ part out so I could grab up some parts, and I hit the jack pot today. A guy up in Plainfield is doing a V-8 conversion for a guy who had a 4 cylinder and blew the engine because he was pushing 36's and towing a jet ski to the mall. He sold me the complete head pipe with the cat and both O2 sensors for $25!!!!! I can sell the cat for at least $50, and I'm sure I could sell the O2 sensors for a couple of bucks too since the connectors are different then my YJ. The 2.5L and 4.0L used the same head pipe from 97-99.
I'll probably start this next week, since I'll be out of town this weekend. My question for the TJ guys, is the mini football thing on the front of the pipe a resonator or is it a small cat? I'm thinking of just cutting it out and welding in a straight chunk of pipe, but is it worth the effort? I know I'll have to cut a few slices in the pipe and bend it a little to match up to the YJ cat, but I don't think it should be too hard. The only other hurdle I expect is I will have to lengthen the wires for the O2 sensor, but that shouldn't be too bad.
For the non-YJ guys , the reason this is a worth doing conversion is on a YJ the head pipe goes under the bell housing of the tranny and hangs fairly low. Mine has several good size dents that I can feel are reducing the power. Plus when I make an engine skid I can tuck it up a little higher.