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Does my Jeep need a Cat?

2K views 48 replies 14 participants last post by  Ross 
#1 ·
Years ago my Catalytic Converter was ripped off during a hunt. I didn't replace it I just threw a straight pipe on and welded it. Both O2 sensors are there, no codes but with a straight pipe. Now I have ripped/broken/mangled my muffler for the last time and I'm sick of trying to reweld it back up and together so I'm replacing the rear exhaust and muffler with a new one (Cat back). pretty much my entire exhaust is rotten or rusted except the straight pipe that replaced the Cat, it was a stainless steel exhaust pipe.

My question is since I'm replacing my Cat back, muffler and pipe should I go ahead and put in a cat? I put that straight pipe in years ago and I'm not sure if it improved the power any.. I think it did a little bit. The sound sure as heck got loader and now to the point that its getting annoying and it's hard to hunt in a Jeep that sounds like I'm rolling through the hills in a 9 second quarter mile drag car.

I'm replacing my cat back but since im there should I replace the cat and some of the forward exhaust as well. I know it will improve the sound (quieter) but will it improve gas mileage or help with power due to creating the backpressure the engine originally had? By the way its a 2.5L 4 banner.
 
#2 ·
Cats actual do a good thing and the says you have to have one.

I have ripped my cat off and my muffler (a few times). I now run with just a Cat and my pipe turns down and out just pas the diff skid.

 
#3 ·
with just the Cat and no muffler how loud is it? I was thinking of this but I wasn't sure because I was thinking it would be too loud. I do a lot of Quail, Deer, Elk hunting and I didn't want it too loud plus on the highway it gets really bad, I only have a soft top.
 
#4 ·
You hear when you accelerate hard other than that it isn't as loud as my Super Swampers.

I broke my exhaust right before the Cat about 175 miles into a 600 mile trip. Running with no cat and no muffler is aggravating.

If you are putting around the woods and not on the gas hard it makes no more noise then when I had my flow master on it.

You probably won't be able to sneak up on wildlife in a vehicle regardless of what you are driving.
 
#5 ·
I've run with just a CAT and no muffler for a short time and it is considerably louder without the muffler. I think that would be kind of obvious honestly as that is its' primary function. If it met noise standards without a muffler Chrysler wouldn't have designed it with a muffler to begin with.

The CAT does provide some noise reduction but it's primary function is to reduce emissions and it does so significantly. I wouldn't run without one regardless of my states emissions standards.

:cheers2:
 
#7 ·
I've run with just a CAT and no muffler for a short time and it is considerably louder without the muffler. I think that would be kind of obvious honestly as that is its' primary function. If it met noise standards without a muffler Chrysler wouldn't have designed it with a muffler to begin with.

The CAT does provide some noise reduction but it's primary function is to reduce emissions and it does so significantly. I wouldn't run without one regardless of my states emissions standards.

:cheers2:
When I lost the Cat the noise level increased much more than being just without the muffler.

I ran a flowmaster 40 before and I run Super Swamper tires. The noise level in my Jeep is probably higher than many. I am sure if you have less aggressive tires and a stock muffler running without a muffler would be far more noticeable in your Jeep than mine.
 
#8 ·
I guess what I'm actually getting at here is when I finally lost my CAT I just cut if off and installed a straight pipe in place of it. It's been too long and I cant remember if there where really any improvements to HP or FT-LBS. Plus having the angry 4 squirrels it's hard to make any improvements without dumping some serious cash.

So the place I'm at is this I have all straight pipe to the muffler, the muffler it falling off. Im in a place to actually replace the front pipe and new CAT and put in a new heavier duty muffler and rear pipe. All the pipe on the Jeep is original factory except the piece that replaced the CAT.

Should I just replace the muffler and be done with it? Or should I replace the muffler and install a new CAT?

Remember I'm running with four angry squirrels so every HP counts at the moment till I can do a engine swap and that's not coming for a good long while (I'm still paying for and piecing all the parts together slowly)!

Would the new CAT help or hinder my HP, I drive in the Mountains of West Texas.
 
#9 ·
I guess what I'm actually getting at here is when I finally lost my CAT I just cut if off and installed a straight pipe in place of it. It's been too long and I cant remember if there where really any improvements to HP or FT-LBS. Plus having the angry 4 squirrels it's hard to make any improvements without dumping some serious cash.

So the place I'm at is this I have all straight pipe to the muffler, the muffler it falling off. Im in a place to actually replace the front pipe and new CAT and put in a new heavier duty muffler and rear pipe. All the pipe on the Jeep is original factory except the piece that replaced the CAT.

Should I just replace the muffler and be done with it? Or should I replace the muffler and install a new CAT?

Remember I'm running with four angry squirrels so every HP counts at the moment till I can do a engine swap and that's not coming for a good long while (I'm still paying for and piecing all the parts together slowly)!

Would the new CAT help or hinder my HP, I drive in the Mountains of West Texas.
I have a magna flow cat which I believe is just a straight shot through it so I don't think it is very restrictive at all. If I were to chose one over the other I would choose the CAT.
 
#10 ·
Jeeps actually like backpressure..with that being said. I would never run a jeep without a muffler. My LJ has 2 upper cats (o2s upstream) and one in the rear. I deleted the one in the Rear (no 02 sensors past) and installed a Flowmaster Hushpower muffler and 2.5 pipe. Sounds awesome and has improved throttle response.

My old TJ I removed ALL cats ...I will never do that again. The emissions that came out of that Jeep were horrible on a hot sunny day with the top down. At lights and on the trail I was getting fumes into the Jeep. Replaced upper cat and put Hushpower and 2.5" pipe and was MUCH better.


if you are concerned about loss of HP if putting a Cat in , put a High Flow cat in ... you should not notice much if any
 
#11 ·
The most I was wandering about is whether I really need that back pressure with the CAT and whether it would improve the HP and or gas mileage or not... I'm not really concerned about gas mileage, I mean heck it's a Jeep, it's a brick on four wheels... If I was concerned about gas mileage I would be here cause I wouldn't own one... I'd own a Prius or something... :thumbdown: ...

I'm replacing the muffler no question with a high flow heavy duty welded muffler. But I'm not that concerned about the exhaust fumes as I've actually never had a problem with them entering the cab and that's with a completely busted exhaust leaking all over and at times driving back home after a hunting trip with no muffler at all because it was lost to a rock. My main concern is after I replace the muffler, if I install an new CAT as well would my potential HP go down any?
 
#13 ·
Just throw a cheap cat on you Jeep and be done with it, you can get a Magnaflow for $112. Your Jeep stinks and nobody likes driving behind you. A cat will not hurt or help performance, but will significantly reduce emissions and make it smell better. Plus it is federally illegal to delete the cat on any vehicle that originally came with one.

This is coming from a 2.5L owner with no required emission tests. The Magnaflow cat I installed I could actually see through, so I doubt it is adding any restriction to the exhaust. FWIW my Jeep runs better with a new cat than it did with the gutted cat, seeing as you replaced the old cat with a straight pipe you probably will not see the same benefit.
 
#14 ·
Personally, I find 'backpressure' to be a muffler shop term and mostly nonsense. Mostly but especially in this case. I'm not saying to strip your header or manifold off and have a good time but you're not going to gain anything by getting any so-called high performance exhaust parts. You won't lose anything either so just replace it with an oem cat and or full exhaust.
 
#18 ·
Do you know of a single person that has ever been pulled over and given a ticket for not having a cat? I live in one of the most smog restrictive states possible and I've never met or heard of anyone.
 
#16 ·
I don't have any emission inspection requirements as I am Georgia registered. I had my CJ straight piped and my ram Cummins straight piped and saw no gains really. So there is no need to not have a cat on my vehicles. Plus it is a violation of the clean air act. Never really noticed smog until I moved to california... it is horrible...

That being said, here you go.

https://www.google.com/url?sa=t&sou...seBmeTrfgkclrF1zQ&sig2=Mcov_vbZ9wBMm6vI_O7RMw

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#19 ·
I doubt locals or staties could right a clean air act violation.

I got pulled over in my truck in Massachusetts. The cop looked it over and said I should be glad I lived in GA and gave me some crap for speeding and let me go.

It was straight piped, with a stack, programmer, injectors, and intake.

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#24 ·
Does California not do Emission testing prior to letting you insure the vehicle? Here in Vancouver, CANADA we had Emission testing for years (20 years)..up until 2 years ago they scrapped the program. If you failed the emission test, you get no insurance....
 
#26 ·
Out of curiosity went over to my Buddies house and asked him about the federal side of it. He works for Homeland Security Investigations, prior Bureau of Land Management and council to U.S. Fish and Game.... He laughed at me! No one on the federal side enforces it. He said there's no such thing as the Smog police, It's all BS and that no one could write or for that matter even take the time to write you a ticket on something like that (much bigger fish to fry). But with that said, he said on the state and or local side is different. A Officer or Deputy could write you a ticket if there are local restrictions, laws or ordinances regarding Catalytic converters.

For me I could give two >:). I live in a tiny little village in the mountains of West Texas and am driving a 4 Cylinder, so I'm constantly pushing up hill and battling the wind. My concern is HP Helpful or Harmful. Beside that I also checked with the local, county and state guys. Local PD told me quit bothering them or they'd write me a loitering ticket. The Deputies said as long as it's not stupid loud (it's not) and the state guys said they can but never will. It's dumb, they could issue a ticket, you go to court, the judge asks if this is true, you say yes, judge says you need to fix it... are you going to fix it? Yes sir I will. Ok then, case dismissed. And again they tell me not worth their time.

Basically, not to sound like an :thumbdown: but the whole law thing doesn't matter down here. This issue for me is purely based on performance and the ability to get down the road as efficiently as possible making the most HP as possible to get through the pass and up those dang hills!
 
#29 ·
Basically, not to sound like an :thumbdown: but the whole law thing doesn't matter down here. This issue for me is purely based on performance and the ability to get down the road as efficiently as possible making the most HP as possible to get through the pass and up those dang hills!
A properly functioning catalytic converter will not affect HP, all it does is control emissions. If you want to be that guy and say screw the environment and the 5 cars behind you because you don't want to spend the $112 on a cat then do so. You may want to look into carbon monoxide poisoning also just in case you ever get stuck and end up idling in one place for a while.

You have a 2.5L, performance is not a thing and the exhaust on it really does not matter. My Jeep runs just as well with a straight pipe as it does with a cat and muffler.

Jeeps seldom roll coal, so they dont get caught.
its an apples to oranges comparison.
You can easily tell what vehicles are running a cat if you are driving behind them. Even if they don't roll coal, the pungent exhaust smell is a dead give away.
 
#31 ·
Well urban cities get hit harder by the smog. Given, here in the Los Angeles are, we have all the shipping too, but on bad smog days I can't see catalina island from my office. Normally it is clearly visable.

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#37 ·
I ran no cat on a Bonneville that I had because it didn't fit with the headers I installed. (OK, so I didn't make it fit because it already didn't meet CARB standards) The exhaust stunk pretty bad and I wouldn't run a modern car without one again. I'd throw a high flow cat on it and be done. I wouldn't want to be behind a Jeep on the trail with no cats all day. It would suck.
 
#43 ·
I just took off my factory cats my rear pre-cat was bad and I had to replace it with the system from eastern catalytic. The rear cat is in good shape if you want me to cut the pipe and ship it to you I'll let you have it for free you pay shipping.


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