Exhaust down pipe pinch REMOVED ! Pics. Important!
 

There has been much debate why a pinch is in the exhaust down pipe just below the manifold flange on some XJ's (91-early 96 I think). Noticed an XJ in the junk yard sitting low in the front. The pinch is a factory "feature" so the front diff and u-joit clear the exhaust. It was obvious looking at it. With a lift installed this is not usually an issue. I wanted to remove the pinch in mine. Because it is a pre-cat exhaust item, there are no available legal modified replacements without the pinch. Some owners have had shops fab new pipe, but in our jurisdiction, licensed shops do not do this kind of work, as it is installing a non-EPA approved exhaust mod. Found one guy willing for several hundred dollars. But I passed on it.

Here is the pinch:

https://cimg2.ibsrv.net/gimg/www.che...fcd2840a9a.jpg


There is also a second pinch on the engine side you cannot see until the pipe is removed:

https://cimg0.ibsrv.net/gimg/www.che...dfb9861573.jpg


Inside view of pipe showing how the two pinches block flow:

https://cimg1.ibsrv.net/gimg/www.che...49dafd62b9.jpg


Using MAPP gas torch (propane is not hot enough), a good vice, some long rods and a hammer for pushing out the pinches, and four hands (two to work the torch, two to work the metal), we opened up the pipe pretty good:

https://cimg9.ibsrv.net/gimg/www.che...0d652b9ce9.jpg


Here is the outside shot of the pinch removed:

https://cimg8.ibsrv.net/gimg/www.che...d0147605d4.jpg

Flow is greatly improved! A 12 mile test drive indicated a more responsive engine, especially when really stepping on the gas. Also, it seemed to run a bit cooler. Drive was during 80 degree ambient temp. Gauge seemed a bit lower on the hills.


Here's the basic set of tools:

https://cimg3.ibsrv.net/gimg/www.che...5f13445649.jpg


Pipe removal tip--cut a slot in the cat inlet pipe with a power cut off saw. See pic. The clamp on last installation crimps the pipe and makes sliding off the exhaust pipe nearly impossible.

https://cimg4.ibsrv.net/gimg/www.che...d19f7338f0.jpg


After reassembly and engine start up I noticed a small exhaust leak at the cut. So I removed the clamp and got out the welder and welded up the slot and ground it smooth before reinstalling the clamp again.

https://cimg7.ibsrv.net/gimg/www.che...f5f974d27d.jpg

Project finished! Took about 4 hours. Some of that was wasted trying to separate the pipe from the cat. Until I got the idea to cut the cat extension. Then it all came right apart.

Of course you have to remove the O2 sensors and work the pipe out of the rubber center hanger and stuff. But you can figure all that out yourself. I also had to remove the two rear hangers on the rear exhaust pipe. But no big deal. All went back together quickly and smoothly.

Cost was nothing other than time. If I were installing an upgraded manifold with 2 1/2 inch outlet, I would have a new pipe fabbed instead of beating out the pinches in the old one. But that is another project for another day with another dollar. Until then, this seems to be a big improvement at no cost.

Noticed same pinch in my 98. Good job getting it out.

This is factory? i thought i was just too deep in the FLEX ZONE!

It's factory. I thought there was some reason for this

I'm doing rod bearings in my 99 with the engine still in the jeep, pulled the pan an it's a clear shot at that down pipe. Mine looks like it's damn near shut! I was thinking of doing what you did here. Good idea on the torch method!

Give it a try since you have so much out already. Remember, use MAPP gas. Its a lot hotter than propane. Once it gets nice and orange/red, the metal is pretty easy to pry and pound out. We held the pipe in a large vice. But also used some wire wrapped around it all just in case the pounding popped it out of the vice. Its kind of a large hot piece of metal to catch if it gets loose!

Good thinking, I have done it with acetylene, never thought of mapp gas for anyone to do it though.

Yes, factory.

To heat up the catalytic converter sooner.

I just wonder if heating it red hot will harden it and make it prone to cracking like our headers

you can always use an oil soaked rag if youre worried about it to quench it

WTF haha

Quenching it will harden it. Let it cool slowly.

Yeah mom thinking backwards... Sorry

Stupid question, hur dur. Why not just put a hole in the pinch and let it leak out under the hood? Seems like kind of a pain in the *** to do all that....

Seriously, stupid question, just curious.

No lie..... very stupid question. Let's take the 2 most logical answers to your question. Exhaust leaks sound like ****! Not to mention if a hole is drilled it will whistle...... and #2 because c02 can kill you after leaking into the cab of your jeep.

I can also add that a direct blast of exhaust can also start a fire. Plenty of **** to catch on fire under the hood.