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Unread 05-22-2012, 11:30 AM   #16
dest
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After running muffler-less for quite a while if you really want it loud just cut it off after the cat. You'll be able to tell how loud it is and make a decision from there. I've since put a dynomax exhaust on it and I think it's quieter than stock but it has been a while since I've had an exhaust on it...

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Unread 05-22-2012, 12:37 PM   #17
98XJmtar14
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Correct me if I'm wrong please because I might be crazy but like in_motion said if you were to just do straight pipe it would be loud and sound pretty decent I would think but I wouldn't do 3" pipe. Now this is where someone can tell me if I'm crazy or not because I might just have this all wrong but it makes sense to me...If you cut off everything from the just after the cat back and did straight pipe then depending on the size pipe you could still retain your back pressure. The way I see it the back pressure is the speed that the exhaust exits the vehicle completely so the muffler (pardon my crap metaphor) acts like an accident on the highway it slows everything down a bit but not completely so it keeps moving but it backs things up a bit. So assuming that that metaphor is correct if you were to use smaller pipe the exhaust wouldn't escape as quickly so the back pressure would be at least somewhat retained and you would get pretty freakin' loud exhaust that I think would still sound good.

I guess thats more of a question to you more wise jeepers and then if I am correct then an answer for the OP on what I would do, and personally I've wanted to do straight pipe with no cat or muffler just to piss everyone off lol but thats just me!
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Unread 05-22-2012, 01:44 PM   #18
sAe23
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Quote:
Originally Posted by nwpipelayerxj View Post
You can take cat off anywhere without emission testing. Lots of places. Also, yeah the CO gas thing is stupid. BUT, if "I" were him looking for a little louder sound, I would take off everything behind the cat, and put a 90 sideways or straight down, then he still has all his o2 sensors hooked up and no thrown codes. Just a slight loss in back pressure. Best of both worlds. Just my .02
It is a crime under US Federal Law, punishable with a fine up to $25000, to remove a functional Catalytic Converter, and all emission control devices installed by the factory must remain on the vehicle.
Technically, Puerto Rico is subject to US Federal laws...
But, as some might say, it's only illegal if you get caught

As for the SOUND, IMHO any stock motor does NOT sound "cool" w/o a muffler.
You need an appropriate Camshaft, and preferably EIGHT cylinders!

Also, some might argue that insufficient back pressure might contribute to burnt exhaust valves
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Unread 05-22-2012, 03:29 PM   #19
Diamond-x
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I'm used to the California popo where a modified exhaust is good for a fix-it ticket, all they need to do is take a quick look under the car. If it looks modified, you get the ticket. As previously mentioned it's also disrespectful to drone around town.

OK, OK, I'm off the soap box....

The 4.0l engine, or any engine for that matter, requires back pressure to build torque. If you were to simply remove the cat and muffler and run a straight pipe, your engine would run like crap and would have little to no low end torque. Also, with a very short muffler-less exhaust, cool air can flow backup the pipe and warp your valves when the motor is shut off.

So, to recap: There is nothing good that can happen if you remove your cat/muffler. Except it sounds neat-o to a teenager.
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Unread 05-22-2012, 04:28 PM   #20
kg4kzv
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Anyone tried the DynoMax VT. I like the idea of it if it works. I hate the droning that comes with most performance mufflers. Also it seems like it would be stealth like when your not standing on it.

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Unread 05-22-2012, 08:08 PM   #21
BlueRidgeMark
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Quote:
Originally Posted by Azzy View Post
CO leakage into the cabin of the jeep is obnoxious no matter where you live. So is the brain damage that comes with it.
Yes, and sometimes that brain damage comes in the form of having your skull plastered all over the road or a tree because the CO put you to sleep behind the wheel.


Running with your exhaust dumping out somewhere under the vehicle is just plain....



(get ready for it)


STUPID!!





Quote:
Originally Posted by Azzy View Post
Either get an aftermarket exhaust setup and do it right, or dont bother.

Yep. Aftermarket can be a great thing.

Butchering your exhaust system because you think it will sound "good" is just asking for a damaged engine or worse.
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Unread 05-23-2012, 03:42 AM   #22
WindsorRenegade
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Quote:
Originally Posted by Azzy View Post
CO leakage into the cabin of the jeep is obnoxious no matter where you live. So is the brain damage that comes with it.

Either get an aftermarket exhaust setup and do it right, or dont bother.
Hey; I never said it wouldn't hurt your brains. I agree with you 100%.
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Unread 05-24-2012, 08:52 PM   #23
merdock69
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If you take your exhaust off then the engine will suck cold air in the hot exhaust valves and they twist like pretzels!!!!

Just kidding... Don't be stupid, just buy glass packs or have the muffler shop install a dump before the cat....
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Unread 05-25-2012, 08:35 AM   #24
park308
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So question if I were to take off my cat and install the flowmaster muffler would that not be good or could I take out the cat. Right now my muffler fell off and I have bought a new muffler to install but I think the cat is clogged/not working right
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Unread 05-25-2012, 08:44 AM   #25
Jeff9
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I don't really understand what's to gain by taking off the cat. Not like someone is going to stick his head under your jeep and say "wow cool bro!"...there are plenty of legal mufflers that sound great.
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Unread 05-25-2012, 08:56 AM   #26
park308
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It rusted and I don't have the funds to buy a new one so my question is will it affect the motor in any negative way I am not trying to sound look cool I am trying to make it a dd all I want is functionality
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Unread 05-25-2012, 09:27 AM   #27
Pats94
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Depends on the year. It won't affect anything except emissions on older ones. Just try to get 1 on as soon as funds allow.
You may be able to offset the cost of a new catalytic converter by scraping the old one. They will give you money for used catalytic converters.
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Unread 05-25-2012, 09:28 AM   #28
jeepkid03
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Quote:
Originally Posted by park308 View Post
It rusted and I don't have the funds to buy a new one so my question is will it affect the motor in any negative way I am not trying to sound look cool I am trying to make it a dd all I want is functionality
You will set a Check Engine light. I'd just run one of these. It even has the O2 sensor bung.

http://performance-curve.com/425225-...nvertero2.aspx
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Unread 05-25-2012, 09:40 AM   #29
park308
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Thanks I will probably be able to afford that one I have a 91 XJ 4.0
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Unread 05-25-2012, 09:57 AM   #30
dagr8tim
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*IF* I were going to ignore the legal questions, I'd replace the cat with a thrush glasspack style muffler, and put a 45 degree turn down coming off the muffler.

I've often wondered what an XJ would sound like if you put a glasspack where the cat is and then ran a decent muffler. After the glasspack burns out, it would basically be a resonator tube.
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