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Old 07-06-2011, 09:03 PM   #1
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Running without catalytic converter?

Where I live there are no emissions requirements. I will have to replace a leaky exhaust manifold in the near future, would removing the cat converter and running straight pipes help my performance any. I have the 2.5 4 banger and every ounce of power gained would be a help. My thoughts are to put on a header and pipes with no cat. What are your thoughts on this?

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Old 07-06-2011, 09:07 PM   #2
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good high flow cats do nothing to limit power. keep it on.

if you need more power put in lower gears

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Old 07-06-2011, 09:12 PM   #3
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Check out summit or jegs or catalogs like that a low restriction cat can be as cheap as $30
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Old 07-06-2011, 09:21 PM   #4
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Im going to do a regear in the future, just wanted input on removing cat to help. Why keep the cat if emissions are not in play? Even a free flow cat is going to be more restricting than none at all, correct?
I am a Jeep noob, so bear with me on these questions... Is the stock 98 2.5 cat good enough to leave on if I dont have to?
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Old 07-06-2011, 09:27 PM   #5
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Well I am by no means a engine guru. But a certian amount of restriction is needed how much on your engine I'm not sure but straight open is not optimal for a driver. Also I have heard on sub zero days it's possible that parts cool too fast and engine damage is possible
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Old 07-06-2011, 09:34 PM   #6
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Didnt know bout things coolin causin problems, thanks for the info, thats why I asked... I'm 42 lived in north Ga all my life, I cant remember EVER having a sub zero day though. We do see some a few days each winter in the teens and maybe a handful in the single digits, but that is all.
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Old 07-06-2011, 09:52 PM   #7
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I would say it would have to be extreme to bend valves. But I have heard stories. Back pressure is imporntant for a engine aswell I am more experienced in 2 stroke twins. And exhaust is a very strong factor in how they run
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Old 07-06-2011, 09:58 PM   #8
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not having a cat is still a requirement even if they don't check for it. fyi it's a $2500 fine and all it takes is a police officer to smell your exhaust fumes and pull you over to check. leave it there. it's not hurting anything and you may gain 1hp. not to mention the cel that will be lighting up.
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Old 07-06-2011, 10:08 PM   #9
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not having a cat is still a requirement even if they don't check for it. fyi it's a $2500 fine and all it takes is a police officer to smell your exhaust fumes and pull you over to check. leave it there. it's not hurting anything and you may gain 1hp. not to mention the cel that will be lighting up.
You need to realize you are the minority here. I ran full 3 inch CATLESS straight pipe in my wrx in Portland, OR and never got caught AND passed emissions with no question. I dont know how much good it will do in a jeep but in the import tuner world, catalytic converters are not In the picture. A well tuned catless setup will smell THE EXACT same as a setup with cats. If a catless setup stinks then either the fuel map is very conservative or the tune just plain sucks.
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Old 07-06-2011, 10:11 PM   #10
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To the op. If you rid yourself of your cats, put In a resonator or 2, if they do check all they will want to see is something that resembles a cat. And it will quiet it down alot
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Old 07-06-2011, 10:13 PM   #11
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You need to realize you are the minority here. I ran full 3 inch CATLESS straight pipe in my wrx in Portland, OR and never got caught AND passed emissions with no question. I dont know how much good it will do in a jeep but in the import tuner world, catalytic converters are not In the picture. A well tuned catless setup will smell THE EXACT same as a setup with cats. If a catless setup stinks then either the fuel map is very conservative or the tune just plain sucks.
i guess it's up to the op then if he wants to spend the money on a custom tune then remove his cat and have it all be for nothing. a jeep is not an import tuner car that might respond to this type of alteration.
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Old 07-07-2011, 07:39 AM   #12
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Originally Posted by kshaws21 View Post
Where I live there are no emissions requirements.
Do you live in the United States?
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Old 07-07-2011, 10:10 AM   #13
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Actually I live in northeast Georgia. Locally we do not have to have an inspection. I am 42, I can remember when I was a teenager we had emissions inspections and my dad always had to have that sticker on his windshield, but that was cut out in the late 80's around here. I know in Atlanta they have to pass emissions testing, but locally where I am we do not. I know running without cats in Georgia isn't quite legal, but I figured since I NEVER have to get inspected, it might be worth looking into. I have decided against it after reading some of these replies, that I why I joined this board to begin with...
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Old 07-07-2011, 10:39 AM   #14
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Ya there isnt much that can be done to gain any power back other than regear. Exhaust, intake, and chips wont put you anywhere close to what gears can do for you.
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Old 07-07-2011, 12:42 PM   #15
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Originally Posted by kshaws21 View Post
Actually I live in northeast Georgia.
...
I know running without cats in Georgia isn't quite legal, but I figured since I NEVER have to get inspected, it might be worth looking into.
Since you live in the United States, catalytic converters are required under federal law.

http://www.epa.gov/oms/cert/factshts/catcvrts.pdf
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Old 07-07-2011, 02:26 PM   #16
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BAH exhausts are for girls... open header ftw- (this was right after i swapped my header and was making sure i had no leaks didnt leave it like this lol, altho i did get it on the highway for a few miles!)
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Old 07-07-2011, 04:36 PM   #17
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Ever wonder WHY the cats are used?

Without one you can be proud of yourself ---
Just call yourself "BABY KILLER!"
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Old 07-07-2011, 04:43 PM   #18
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This is why I love having old stuff....no cats required
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Old 07-07-2011, 05:01 PM   #19
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Ever wonder WHY the cats are used?

Without one you can be proud of yourself ---
Just call yourself "BABY KILLER!"
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Old 07-07-2011, 11:38 PM   #20
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Ive run every vehicle with and without cats... had a 92 chevy k1500 4x4 with LT1 Corvette engine long tube headers into stud plugs (if anyone knows what they are) I even cut the cats off my 2002 Tahoe Z71 for acouple of weeks... I am willing to lay money down and bet your jeep will run much better WITH the cats...its the backpressure it needs... now you can cut your muffler off thats fine and dandy but cats id leave.
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Old 07-08-2011, 12:49 AM   #21
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BAH exhausts are for girls... open header ftw- (this was right after i swapped my header and was making sure i had no leaks didnt leave it like this lol, altho i did get it on the highway for a few miles!)
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Old 07-12-2012, 07:17 PM   #22
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Originally Posted by kshaws21 View Post
Im going to do a regear in the future, just wanted input on removing cat to help. Why keep the cat if emissions are not in play? Even a free flow cat is going to be more restricting than none at all, correct?
I am a Jeep noob, so bear with me on these questions... Is the stock 98 2.5 cat good enough to leave on if I dont have to?
what part of north georgia are you from? i live in dalton ga, thats about as far north georgia you can get haha.

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