Add a little punch to your Jeep's catalytic converter.

For those who have strokers or heavily modified 4.0L's then you likely know there ARE performance catalytic converters out there for under $100 at Summit Racing, Jegs, etc so I'm not going to go into those alternatives. I will say that if you are going to run your XJ on the street then you should get one of those especially if you have EPA Nazis or have to pass SMOG checks for vehicle inspections. There is no real disadvantage to running a good performance cat - face it: You're driving the equivalent of a brick with wheels. You'll never notice the .001% decrease in accelleration unless you've turned it into an all out street rod. (Cherokee Warrior is the only one I know of who's really taken that job seriously.)

Having said that - sometimes we just gotta make a choice between the cash in our wallet buying Jeep parts... or groceries. When those days come - this mod will allow you to salvage your clogged up cat's shell and stay on the road long enough to save some green for a new cat. It's also a little something for those who have a 2 1/2" cat back system and/or a header and who go offroad in grassy areas where hot converters are a genuine fire danger.

If you lived where no converter is required... then you could simply install a 'test pipe' which is nothing more than standard pipe to replace the cat that has flanges to bolt in where the cat goes. Early Canadian XJ's once had a 'resonator' that would bolt right in where your cat is located but unless you happen to have one layin' in Uncle Fester's barn you're outta luck. It's cheaper to buy a new converter than beg some old parts scrounger for the last 1989 XJ factory resonator in his OEM parts collection. On the other hand... should you need a "converter-like" device installed in your exhaust that can get you back and forth to work temporarily or for, um, going to offroad vehicle shows that require totally stock appearing exhaust systems then you can use this substitute, or "Copy Cat".

NOTE! These will NOT pass a sniffer test for vehicle inspections!

If your state has visual state inspections I am NOT suggesting you save $40 or more by making one of these from your old cat in order to pass a visual state inspection, nor am I suggesting you violate any laws.

These are intended ONLY for use OUTSIDE THE U.S.A. or for OFFROAD USE ONLY to, um, 'enhance your off road vehicle's original exhaust system appearance" for , um, 'OFFROAD VEHICLE EXHAUST SHOWS'".

Method #1 - I'm just bored and my cat is clogged up.

- Remove your old cat, punch the crap outta the interior, reinstall. Works just as well if your cat's shell is in good condition plus ya don't have to go buy anything other than what it takes to put your exhaust back together. Do not breath or eat the platinum chunks that come out of the cat, no matter how tasty they appear with a little catsup.

Method #2 - My cat got in a fight with a mean ol' rock.

In case your exhaust got mashed up - here are the part numbers for the flanges, etc that fit the converter to 'ess' pipe from the exhaust header. These stayed the same for several years - but - you should check that they fit your year XJ before breaking out the welder.

Parts List for 1990XJ:

  1. Exhaust Flange (NAPA #31914 fits 1990 XJ w/ 4.0L)
  2. Exhaust Catalytic Converter Gasket (NAPA # F-10076)
  3. Exhaust Pipe 2 1/8" OD (to fit Exhaust Flange)
  4. Exhaust Clamps.
  5. Someone's old clogged up catalytic converter. Same approximate exterior dimensions. I cut the pipe ID out to be larger to fit my exhaust pipe's OD and a friend just welded that right to the pipe. (Note: If it's a good used converter... ya don't need a copy-cat. Now do ya?)

Note! This article is provided for informational purposes only and applies ONLY for people who live outside the United States or wherever catalytic converters are NOT required.

Removing or disabling your catalytic converter in the United States where it is required is bad, bad, BAD (and very ILLEGAL)! According to the Yu-Ess Gubbamint: Small children will kick you. Babies will cry. Squirrels will stop burying their nuts in your back yard. Old ladies will poke you with knitting needles. Your parents will leave town in shame. And if you perform this modification in the United States... members of the Sierra Club will visit you in the middle of the night, kill you (with environmentally friendly, soy-based butcher knives) and later serve your corpse at a Demokrat party fund raiser.

Take this warning seriously! Removing or disabling your catalytic converter is something to be done for OFF ROAD USE ONLY OR when the vehicle is to be driven OUTSIDE THE UNITED STATES.

Now, if you are a Bad Monkey, that's your business! Here... Have a banana.

Locate an old exhaust system with a decent looking cat of suitable size. A sawzall makes short work of cutting the old rotted pipe off salvaged cat.

Do all of this work outside and do NOT breath in the dust that is stirred up from this work! Rust and platinum are not a combination you want floating around in your lungs...

The quickest way to gut it! A heavy steel post hole digger demolishes the innards and slices off the air tube inside the cat.


Note that converter's inlet/outlet ID has been cut to match OD of test pipe in next photo.

"Test pipe" made from 2' length of pipe & flange.

"Test pipe" inserted into gutted cat ready for a friend to weld it up. After that you're ready to install.


If you have pics of your own repairs or can suggest other methods - please contribute your ideas (and pictures) to this article!

Revised on: October 17, 2006

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