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Old 08-25-2011, 09:11 AM   #1
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Downsides to removing the cat?

I'm fairly sure the cat on my '92 4.0 is at least partially clogged. Considering the Jeep is a weekends only vehicle, and doesn't need to pass emissions, is there any downside to simply gutting the cat?

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Old 08-25-2011, 09:13 AM   #2
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The nasty, God-awful sound it will make.

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Old 08-25-2011, 09:20 AM   #3
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The upside is you can sell it for $$$
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Old 08-25-2011, 09:21 AM   #4
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Get an infrared heat gun on it and make sure it's clogged first.
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Old 08-25-2011, 09:24 AM   #5
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Get an infrared heat gun on it and make sure it's clogged first.
What temperature should a normal one read, and what temperature would a plugged on read?
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Old 08-25-2011, 09:34 AM   #6
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If the outlet of the cat is 200 degrees or more hotter than the inlet (can be up to 500), there's a problem.


Edit: A bad cat can also be checked with a vacuum gauge to see if there's more backpressure.
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Old 08-25-2011, 09:42 AM   #7
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The outlet is hotter than the inlet? I would have figured that to be the other way around.
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Old 08-25-2011, 09:47 AM   #8
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The outlet (end furthest from the motor) will be hotter due to the inefficiency in the cat and build up of exhaust gases as it tries to "push" through the "bottleneck".
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Old 08-25-2011, 10:04 AM   #9
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Cut it completely off. 4.0 sounds mean on straight pipes
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Old 08-25-2011, 12:42 PM   #10
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As long as you don't have emissions or safety insoections, there is no down side. I have not had a cat or muffler in 2 years. If I could post a sound clip of mine running I would but I can't from my phone.

Legally you need to have one on, its a very hefty fine from the epa if they ever finds out.
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Old 08-25-2011, 12:48 PM   #11
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I haven't had one on my YJ since I had had it 2 weeks. The 4.2L sounds sounds good without it. But I think I have a exhaust leak before the muffler.
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Old 08-25-2011, 02:20 PM   #12
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I did this exact thing your talking about. My Jeep was sputtering so I figured it was just the cat. So I took it off, hollowed it out and put it back on. First thing, IT SMELLS TERRIBLE ! YOU HAVE BEEN WARNED.
Second the sound is very, very annoying. I like a nice quiet Jeep, not some wanna bee rice burner. My advice is to remove the cat, shake it and see if its loose inside. If your not sure then just put a straight pipe on and see if it rides any better. Don't be stupid like I was and just hollow it out to do it. I will type it again, THE SMELL IS TERRIBLE !
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Old 08-25-2011, 06:01 PM   #13
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If it smells after u remove the cat there are issues that need to be found and fixed. I have 0 smells and have had 0 smells the entire time its been removed.
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Old 08-25-2011, 11:02 PM   #14
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smells are not that bad. I had 4 cats on my mustang and sent them all packing, clears up a lot of power on those cars. As for the jeeps can't speak to but I would be afraid of the sound it would make with out one, get a 'hi flow' one welded in its place.
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Old 08-25-2011, 11:15 PM   #15
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Pop it off and put a high flow on. NA engines you make more whp and wtq with back pressure. Only on a turbo engine would you want free flow but only after the turbo as the turbo is what keeps the back pressure there.

On my 2.5L i had a cat that was blown apart. So i welded in a cat of an 03 S500 benz and a glass pack now it sounds better and runs stronger.
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Old 08-25-2011, 11:21 PM   #16
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Quote:
Originally Posted by crazymike
Pop it off and put a high flow on. NA engines you make more whp and wtq with back pressure. Only on a turbo engine would you want free flow but only after the turbo as the turbo is what keeps the back pressure there.

On my 2.5L i had a cat that was blown apart. So i welded in a cat of an 03 S500 benz and a glass pack now it sounds better and runs stronger.
This is part true but at certain rpm no cat would be beneficial. The back pressure gives more HP and torque at lower rpm but less back pressure would give you more at higher rpm iirc
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Old 08-26-2011, 08:06 PM   #17
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Downsides? You'll choke yourself out when you stop. Hefty fine if someone finds out.

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The upside is you can sell it for $$$
HAH not really. Most places will only pay about $30 for a good used cat. If it's bad then even less!!

And don't even think about removing the platinum inside, you'd need an entire refinery just to do so.
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Old 08-26-2011, 08:39 PM   #18
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Honestly the smell is not that bad. People were able to deal with the odor for many years before cats were installed. I have a 70 Buick with a 455 and everytime I stand behind it running the smell makes me smile. I also took the cat of my TPI 350 GTA and the smell is minimal at most. As far as sound goes, get a nice muffler and that will take care of that, it will not sound like a fart can ricer. Even if your car is considered "historic" or does not have to pass emissions in your state, if your car was built with a cat, it is required that you have one and you will be fined for taking it off. Like others suggested above, a good high flow cat is the best answer for you and the environment.
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Old 08-26-2011, 09:57 PM   #19
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I ran my 89 for 3 years without a cat. Quiet, no difference at all in power. Recently it wouldn't pass the inspection for that reason.....$160.00 later, it now has a cat installed. No difference in sound or power.....but my wallet is $160.00 lighter.
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Old 08-26-2011, 11:03 PM   #20
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I've never been hassled about it trying to get a sticker and I live in mass....
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Old 08-27-2011, 09:16 AM   #21
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I put a magnaflow high flow cat on. It was a direct bolt on.

The thing about air flow is it's only going to flow so well with the stock intake. If you opened it up to a cold air intake, then did the high flow cat, then a high flow muffler like the flowmaster 44, you'll see a bit of difference in the power and definitely a good sound difference. I have this set up on my Jeep and it was definitely worth it to help the engine breath better.
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Old 08-27-2011, 10:33 AM   #22
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There is no down side! I've done it and still passed emissions. Friends have done it and passed. If the rest of the Jeep is running properly, won't be a problem. I understand you don't have emission testing in your area. Do you have vehicle inspections? Do you off-road? Here in Washington, we're required to have a muffler or spark arrestor at the very least to go off-road.
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Old 08-27-2011, 12:14 PM   #23
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I say replace it and do mother nature a solid...just my .02
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Old 08-27-2011, 09:50 PM   #24
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This is part true but at certain rpm no cat would be beneficial. The back pressure gives more HP and torque at lower rpm but less back pressure would give you more at higher rpm iirc
Yes you are right but a jeep engine isn't really a high reving engine. Also if you are wheelin you would want that down low power but if you are diving on the highway you would want that top end.
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Old 08-27-2011, 10:11 PM   #25
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If you don't have to pass emissions, cut it out and replace it with a piece of pipe.
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Old 08-28-2011, 08:37 AM   #26
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I say replace it and do mother nature a solid...just my .02
I like how you made them use their brains with a decimal instead of words for your 2 x. 01
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Old 08-28-2011, 09:01 AM   #27
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I say replace it and do mother nature a solid...just my .02
At emissions testing time, my Jeep passed with flying colors w/o a cat. So as far as mother nature and the government is concerned, I am doing "solid".

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I like how you made them use their brains with a decimal instead of words for your 2 x. 01
"them" not us? I thought we were all in this together. Who exactly is "them", people you disagree with? That must make "us", people who disagree with you.
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Old 08-28-2011, 09:55 AM   #28
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At emissions testing time, my Jeep passed with flying colors w/o a cat. So as far as mother nature and the government is concerned, I am doing "solid".



"them" not us? I thought we were all in this together. Who exactly is "them", people you disagree with? That must make "us", people who disagree with you.
Well said and so true.
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Old 08-30-2011, 06:31 AM   #29
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Man, i wasn't disagreeing with anyone ab the emissions thing. And i could have used "us", though it seems of little importance. Sorry for offending you if you didn't understand what i was actually saying. (Two cents)
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Old 08-30-2011, 04:53 PM   #30
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I cut off the stock cat and muffler that was on it the day I bought my 95 YJ. Its gone and I'm glad! I went out and got a MagnaFlow muffler and welded it on. It sounds good and I have no problems with it. I say GO FOR IT!!!

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