TJ headpipe in a YJ

[kirksjeep]

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.

[Tsunami]

if you want, i can swing by and you can take a look at mine

[Axle]

Starting from the manifolds, each one has a cat, then they meet the head pipe where there is a resonator, then the muffler, and so on.

[BayouGold]

...& the thigh bone connects to the knee bone, & the knee bone connects to the shin bone. sorry, couldn't resist.

[kirksjeep]

Starting from the manifolds, each one has a cat, then they meet the head pipe where there is a resonator, then the muffler, and so on.

The 97-99 collect in the manifold and then enter the head pipe.  The 00 and later have two connections at the head pipe/ manifold.  I did a little research and it is a cat, but it is a low restriction set up.  The pipe goes from 2 1/4 prior to the mini-cat to 2 1/2 after the mini-cat.   Everything I have read about these is that they are not worth the effort to cut out, since they shouldn't change the performance.  The 99's are the first year for these mini cats. 

Here is a link to a write up of the YJ problem and the TJ install.
http://www.virtualjeepclub.com/showthread.php?t=9091

This one doesn't show the mini cat, but it would be at the leading edge of the oil pan.

[PaulW]

so did it fit?

[kirksjeep]

It fits in my garage ,  I havn't had time to put it in with the XJ project and working on my Pop up camper.  I'll get it in before the next trail ride.

[PaulW]

sweet

[kirksjeep]

I started this conversion today.  I un-bolted the YJ pipe and pulled it out, cut the cat off of the TJ pipe and then everything else was down hill from there .  The flange that bolts to the manifold was a differnt so I cut the flang off of both and tacked the YJ one onto the TJ pipe.  Then the angle to go around the front of the oil pan was WAY off.  I cut the TJ pipe just before the mini-cat and started modifing it to fit.  I made about 10 slices to make the bend and had to add about 2 1/2" of straight pipe to make it work.  I am about 90% done with this first part, but decided to break since welding and grinding in the heat sucks. 

I know that when looking for a stock head pipe the 91-92 versions are differnt, and I am not 100% sure why, but I am thinking it has to do with the anlge of the manifold exit.  This is definitly going to be much harder then I expected.

[BlacXJeep]

aww booo! you were so excited about it earlier too. I'm sure you will get the job done though.

[kirksjeep]

aww booo! you were so excited about it earlier too. I'm sure you will get the job done though.

Wosrt case I'm out $46 for a new one to replace the dented one I had, plus I'd be out $25 I paid for the TJ one.

[kirksjeep]

I made more progeess today.  I now have all of the pipe done except the last foot or so and the flange.  It turns out the inlet to the cat is 2 1/2" but the stock YJ pipe was only 2".  For my custom creation, the first 18" or so are 2" and then it transions to 2 1/2" which will flow all the way to the cat and the cat back is already 2 1/2". 

[kirksjeep]

I like to make mods that only a Jeep expert would notice.  The pipe is going to be tucked up as high as I could make it, and will end up about an inch higher then the TJ's.  Since it will be up so high no one will ever see it, but a YJ guy will notice that it's now hanging below the transmission. 

It's kind of like my CB mount.  I wanted to put the CB where the Ash tray/ cig lighter was, so I spent 2 days making a bracket to move the ash tray/ cig lighter under the radio and mount the CB under the heater controls.  It came out so clean even YJ guys don't notice, which was the idea. 

[kirksjeep]

I used a 2 1/2 hold saw and drilled out the mounting flange for the 2 1/2 pipe to go into the CAT.  It took a while since it was 1/4" thick steel.  I got everything welded up and gave it a quick shot of header paint and went to mount it up.  Everything went in ok, but the O2 sensor wont fit.  There is not enough room for the sensor .  I tried making it fit and cracked the body of the sensor, so now I have to buy a new one and weld in a bung, plus plug up the existing hole .  The O2 senser that I broke was 17 years old and should probabaly be replaced anyway. 

This has been a 3 day project and I'm still not done.  This was much more time consuming then I ever expected, I'm just hopping it will work as planned.

[kirksjeep]

I finally finished this project.  I found that advance auto, and auto zone do NOT carry O2 senser bungs and Midas ( who claims to build custom exhausts) did not have any either.  I found some at Bumper to Bumper across from base and they also had the plug for the stock one too .  I also bought some stuff from permatex that is for sealing exhaust systems and fixing cracks.  It goes on like a paste but dries hard.  I used some on all my welds just incase I had a pin holes. 

When I took it for a test drive I noticed the Jeep doesn't have to work as hard.  I couldn't feel some huge gain in power from the seat of my pants, but I didn't try to do a burn out or anything.  For example, I slowed down to about 25-30 MPH to let a car in front of me turn, and I was in third gear.  Normally I would have hit the gas and realized the engine was bogging down, and shifted into second.  This time I stepped on the gas and the Jeep accelerated with no bogging down and I never had to shift.  It almost felt like I re-geared the axles. 

Now that that is done, I already started the intake manifold swap.