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Cat replacement, removal, or conversion to straight pipe?

hockeyfan_019

NAXJA Forum User
I am quite sure a flame-fest may ensue, but a couple of questions here regarding replacement or removal... Please don't start all green-vs-polluting BS here though, I understand that without a CAT the emmissions will be worse, IF the engine is running perfect mixture, the operating temps are in range, and the humidity is correct... But regardless, I imagine that it STILL will not be as bad as my lawnmower, motorcycle, gas grill, weed whip, chainsaw, or certainly an F350 superduty diesel or city bus!

First, the scenario. '89 XJ 4.0l with TONS of miles... Cat still has "pressure", ie no holes, but it sounds like theres a steel baseball trapped inside that's trying to get out...

Option 1: Remove the POS, replace with straight pipe. Advantages, lower cost than replacement, quick fix (section of new straight pipe up the the cut on either end of the old section, and 2 hose clamps), no more potential for the thing to go bonkers on the inside. Disadvantages, poor joint integrity (how much do those clamps hold anyways), having to find a new section of pipe with the correct end geometries (like "muffler man" hasn't been asked for that before), and emmissions potentially get worse. BTW, no emmissions checks in Michigan any longer.

Option 2: Replacement, muffler shop job. Advantages, no labor, best strength, maintains emmissions. Disadvantages, high cost, potential for breakdown later on again.

Option 3: Aftermarket CAT replacement. Advantages, better cost, maintains emmissions (if with the right one I guess). Disadvantages, probably medium strength, probably less durable than the "Tuffy" type, install labor probably has some swearing-factor, and online part quality is a crapshoot.

How have you guys solved this problem?

Thanks,
Tom
 
Option 1: Remove the POS, replace with straight pipe.
If you drive this vehicle on the street, it may be difficult if not impossible to get a safety sticker without the cat.

Option 2: Replacement, muffler shop job.
Muffler shop job. It will be (hopefully) done well and you don't have to do it. There is almost no advantage to a "free flow" aftermarket cat as the stock cat is very free flowing already. It will cut down on emissions. We should all do our share in that department. They do last a long time so that is really not an issue.

I took mine to Midas and had them slap a new one on. Didn't cost that much. (I don't even remember how much it was.) Works fine. Lasts long time.

RR3
 
cat

I just bought a new cat off ebay for $37. replaced mine for a grand total of $65 that's with cat, pipe, clamps,etc. It's made by Catco search on ebay for one. Oh it's 2.25" inlet/outlet for factory tubing. My rattle is gone and the engine breathes way better. I have a pre OBD 2 XJ.
 
I got a high flow cat from www.summitracing.com . It was cheap and installs easy. Might as well get improved millaege. Keep in mind if you run straight pipe (I wouldn't) where are you going to plug in your no. 2 O2 sensor?

Curt
 
I recently bought a Jeep with the cat already removed. I'm putting a new cat on it ASAP if that tells you anything. The performance is same as any stock Jeep but the exhuast smell is kind of heavy. Replace the cat, they can be had for cheap.
 
Agreed with the above.

Wheelers in general already get a bad enough rap as it is, without lending more credence to it by running cat-less. This provides no benefit, except to the wallet, and does nothing but give the enviro-nazis one more thing to bitch about. We just lost some key wheeling spots to these people. Lets not let them have the ammo to amke things even harder than they already are. Go to a muffler shop and get a cat, it makes sense.
:cheers:
 
h.curtis said:
Keep in mind if you run straight pipe (I wouldn't) where are you going to plug in your no. 2 O2 sensor?

He's got a 91. It only has 1 O2 sensor, on the down pipe. OBD-IIs at 95 and newer got the second O2 sensor.

Having said that, I wouldn't run without a cat either.
 
Okay, I didn't read this whole thing, but I'm going to throw what I'm going to say anyway...

I toyed with the idea of getting rid of my cat after I crushed it on some rocks, I ended up not doing it though for a few reasons, I'm sure they've been listed here...

Now, here's my plan (I haven't done this yet).

Get a cheap, cheap cat and muffler, and put 4 bolt fittings on either end (such as there already is on the forward end of the cat), now, get a decent muffler and cat and make it the same way. Modify the tailpipe to accomidate this new fitting. Boom, instant trail and street exaust, that way you can have a good exaust system for the street, and one that you don't care if you crush for the trail.

A good reason somebody brought up to run a cat...spark resistance! I was thinking originally of running no cat and a cherry bomb (strong and cheap) for muffler for my trail exaust, well taht'd be straight though and if any sparks left my engine..well..they'd hit the ground, not good!

Sequoia
 
my cat was doing the exact same thing as yours, with the steel sounding baseball and everything, so i bought a new one online from i forget where and passed emissions with it the next week.
 
hockeyfan_019 said:
Please don't start all green-vs-polluting BS here though, I understand that without a CAT the emmissions will be worse...

Asking you to (1) obey the law and (2) not give the rest of us a bad name with the enviro-Nazis is not, IMHO, "BS."

Replacement cats are cheap, and they work. You can get a universal fit at any parts store for $50, and Summit Racing sells the Catco direct fit for the XJ. That's a low restriction cat that flows better than your old-style converter.
 
When I put on my gibson my cat was too banged up to keep so we took it out, I ran my jeep like that for close to two years and both years it still passed emissions. I put a cat in it a few months ago and I really noticed a loss in power and it muffled my exhaust down. Took the nice growl out of it. Looking back at it, I wish I'd just stayed without.
 
h.curtis said:
I got a high flow cat from www.summitracing.com . It was cheap and installs easy.

Curt, I'm not meaning to trample on you but I want to explain something. There is no such thing as a high-flow cat. They're the same thing wether they are regular or high flow. The reason being that the amount of precious metal inside the cats (which is what restricts flow, and burns off excess gasses) is regualated by the government, it's also expensive. So no company is going to put any more of that material into their cats than they absolutely have too, and no company can put in less than the government requires. The way to get high flow is to go a size or two larger than your pipe, then have the muffler shop fill in the gap with a weld.
 
Thanks for the comments guys.

I had pretty much already decided upon option #2, but I was curious to see everybody else's solutions and reactions to the question.

I have seen several studies which suggest that emmissions are often WORSE when a cat is installed though. Somebody on the JU site posted a thread a while ago also discussing it I think.

Thanks though,
Tom
 
crimsonride said:
Curt, I'm not meaning to trample on you but I want to explain something. There is no such thing as a high-flow cat. They're the same thing wether they are regular or high flow. The reason being that the amount of precious metal inside the cats (which is what restricts flow, and burns off excess gasses) is regualated by the government, it's also expensive. So no company is going to put any more of that material into their cats than they absolutely have too, and no company can put in less than the government requires. The way to get high flow is to go a size or two larger than your pipe, then have the muffler shop fill in the gap with a weld.

Crap I got ripped off. I saw all kinds of ads for high flow cats. At least I didn't go with Random Technology's one for big bucks. I didn't know all these companies like Summit, Jegs and Random Tech were just ripping us all off.

Oh well, I am getting 3 mpg more and have more low end torque, but I have no idea if it is from my Borla exhaust or what?

Curt
 
crimsonride said:
Curt, I'm not meaning to trample on you but I want to explain something. There is no such thing as a high-flow cat. They're the same thing wether they are regular or high flow.

If you are going to explain something, it would be a good idea to know something about the subject before telling someone else he's wrong.

Compare a Catco hi-flow catalytic converter to the converters that were OEM equipment in the late 80's to early 90's XJs, and you'll see that there is a tremendous difference. Compared to the old OEM stuff, the Catcos are definitely "hi-flow."
 
my cat just started rattling so im going to take it off and put a pipe in for a few weeks to save up money to buy a new one. will my jeep still run good without the cat and what will i do with the o2 sensor for the cat. my jeep is a 1996 4.0 cherokee
 
I just had an educational experience with a MJ. '88(renix) Stock long block/intake, header, stock down pipe, no cat, flowmaster muffler, exhaust exit just in front of the rear tire.(out the right side) In the dark, I could see it was blowing flame out the pipe about 6" when we were on the gas.(In tune and all the sensors working)

Another reason to keep the cat: I think the afterburning effects of the cat will burn that off in the system, and it won't be escaping out to set the grass on fire
 
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