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Old January 30th, 2006, 05:07 PM   #1
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Default zj cat converter

Can I cut the cat out and have a bung welded in for the 2nd o2 sensor? Or will not having the cat in give the o2 a bad reading?
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Old January 30th, 2006, 05:11 PM   #2
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The 2nd O2 sensor detects how efficiently the converter is working. Not having it in or deleting the converter can cause a faulty reading. There is a gizmo that will replace the converter that gives a good signal back to the ECU so it appears the converter is working just fine (I can't remember where you get it though).

Why do you want to eliminate the converter? Is it plugged?
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Old January 30th, 2006, 05:25 PM   #3
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Yes, It is plugged. It sounds like there are marbles inside it.
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Old January 30th, 2006, 06:12 PM   #4
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Sound like it's not plugged but the honeycomb has fallen apart inside it. You could take it off and pound the honeycomb out of it or install a replacement converter for about $100. The converter on my 96 ZJ did the same thing and I replaced it with a Dynomax converter.

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Yes, It is plugged. It sounds like there are marbles inside it.
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Old January 30th, 2006, 06:43 PM   #5
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Quick Question
I have 4 sensors in my cat on my TJ. If I try and hollow it out will it mess with the sensors? I want to take it off but I dont know what I would do with all those sensors
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Old January 30th, 2006, 09:08 PM   #6
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I don't understand this craze with punching cats. At one time it was worth it, back in teh 70's and 80's. But now, cats are flowing so well that most will not notice any performance gains by taking it out. In fact, you will loose torque. If you already have a problem with it then replace it, if you can't afford to replace it then do what you must. I am looking for a reasonably priced cat to install in my CJ. I am tired of all the gas fumes and I guess I am soemwhat of a tree hugger.
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Old January 30th, 2006, 09:43 PM   #7
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You can hug my punched out cat if you want.

I wanted to hollow it because I am cheap and its plugged. Now that I see that I cannot hollow it out i will replace it. Its a dd zj, im hardly looking for performance gains.
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Old February 7th, 2006, 07:30 AM   #8
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Quote:
Originally Posted by Jeeperz Creeperz
The 2nd O2 sensor detects how efficiently the converter is working. Not having it in or deleting the converter can cause a faulty reading.
I have no cat and no codes??? Actually runs fine, if not better after I cut the cat out and put in the FlowMaster...
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Old February 7th, 2006, 08:29 AM   #9
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Quote:
Originally Posted by shawn
I don't understand this craze with punching cats. At one time it was worth it, back in teh 70's and 80's. But now, cats are flowing so well that most will not notice any performance gains by taking it out. In fact, you will loose torque. If you already have a problem with it then replace it, if you can't afford to replace it then do what you must. I am looking for a reasonably priced cat to install in my CJ. I am tired of all the gas fumes and I guess I am soemwhat of a tree hugger.
Even modern cats cost power, that is pretty well dyno proven. And its getting worse with many modern designs placing 2 or 3 separate cats in the system, sometimes right on the exhaust manifold for quick lightoff.

Backpressure also always hurts your power and torque.
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Old February 7th, 2006, 08:33 AM   #10
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Quote:
Originally Posted by shawn
I am looking for a reasonably priced cat to install in my CJ. I am tired of all the gas fumes and I guess I am soemwhat of a tree hugger.
Summit Racing has universal cats for about $55 in many sizes.
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Old February 7th, 2006, 09:07 AM   #11
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Haggar, I once thought so too. You should read this thread my good friend Scooter wrote up. A while ago he convinced me, cats are good to have and not really worth the effort to remove.
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Old February 7th, 2006, 09:42 AM   #12
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I've read his write up. In general I agree with it.

Backpressure and exhaust velocity/scavenging are not the same.

On a brand new (non turbo) vehicle without other exhaust mods, probably doesn't do a lot. On a 100,000k mile cat, getting it out of there can make a pretty noticable difference. When you've put done work on the intake side, done headers, increase pipe diameter correctly, low restriction muffler, etc, then that cat is by far the bottle neck.

On a Turbo vehicle, catalytic converters are the devil himself.

I'd say thats probably correct, the difference between a high flow cat and a test pipe is 5-10 hp for most situations. On my 110 hp motor, I can feel 5 hp. On a turbo car, it can be 25+ Hp + better turbo response.

My personal experience dyno testing smaller high output import engines, there was no loss of torque at low end. Actually a lot of 'rules' about exhaust doesn't seem to always hold true on those engines. We had better performance across the board with a 4-1 header compared with a 4-2-1 with same size primaries.

I think hollowing out a cat is bad, though. Not exactly a high-flow piece of pipe, even when its hollowed out.
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