Has anyone taken off there cat or done any mods to the exhaust for better flow, slight HP gain, etc??

I did a search, but LAWD, I don't know how to use it I guess... gave like a bazillion useless hits.

Pics, write-ups, suggestions are all welcome!

I think it is illegal to remove the cat(s) still on any vehicle. Also what would concern me about removing the cats would be how the oxygen sensors would react or the computer would adjust, I don't know. Maybe some one else knows could answer that. There are plenty of after market exhaust systems out there that allow the exhaust to breathe easier with some performance gains. Some guys just go with a performance muffler and a turn down for a tail pipe as apposed to a full tail pipe.

Very illegal to remove them, Federal law, can only replace them

Plus would not really make that much difference anyways on the 3.7

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MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

Removing the cats, wouldn't make much difference. Installing JBA Headers would make a difference. With that said, the only reason I might consider something like this would be if I needed to replace one or both exhaust manifolds.

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2004 TJ Rubicon.

Removing cats like stated is illegal,$2500 per cat removed,federal law.You will also get terrible mpg's since the O2 sensors will not work right and you will run extremely rich.Also reducing the back pressure to much will actually reduce HP unless the proper internal engine mods are done to take advantage of the less back pressure and that will be all in the high rpm's so either way you will loose low end power.

Just throw a cat-back system on or free flowing muffler of your choice and be done with it.

tjkj,

What did you do to yours? I noticied in the pics of the belly of your KJ that is was modified??

Keith

Removing the cats is illegal as stated before, so don't do it. You will not gain anything, and if you "gut" your cat you will actually hinder performance. Furthermore, with a free-flowing exhaust AND a decat, you will have a NASTY raspy tone to exhaust (think honda civic) ...yes even the V6.

With that said....

When the primary cat is removed, you will show the same o2 levels on the upstream o2 sensor (used for fuel trim) and downstream o2 sensor (used to monitor cat effectiveness). This will cause the ECU to think that the cat is dead, and throw an engine code putting you into limp mode.

You can bypass this a couple of ways.

- install an o2 emulator, a device that mimics a properly working downstream o2 sensor
- install a small piece of tubing that will space the downstream o2 ~3" away from the flow. This will reduce the amount of flow reaching the sensor, which will fool the ECU into thinking the cat is there and working properly.

Honestly though, keep the cats, stay legal, and buy yourself a set of headers!

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-Rich
It must be air in the fuel!

dont think there's any sensors after the primary on the 3 cat systems, atleast there isn't on the 03 models

i've been beating on a car dealer for right at a year because when they sold me my jeep it was missing the primary cat

no engine codes, doesn't run unusually rich, but does seem to lack a small amount of back pressure for appropriate performance over 4k rpm's

we'll see if that changes in a few days when a cat is put back on it

it took alot of phone calls, alot of threats and a bit of time but i now have a check to cover the replacement of the cat, with a new muffler thrown in plus the cost of normal labor for it

and the car dealer was fined somewhere between 2500 and 7500 bucks - apparently one of the EPA investigators visited the car lot and found other vehicles in similar condition

apparently the lot was cutting off cats and taking them to recycling

a good muffler, headers if ya want, will help, but your real performance increases will be further upstream

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03 Renegade (Black)
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