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Unread 09-18-2013, 07:44 AM   #16
Kingr98
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1998 ZJ 
 
Join Date: Dec 2012
Location: Madison, AL
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It seems a little off topic at this point, but my cat problem has been solved.

I took it to a local muffler shop and 30 minutes later, i gave the guy $30. As riot1987 said, he used a sawzall to cut the old one off, and as pageman said, he welded the new cat on.

I could definitly see light through the new cat, but only darkness through the old. I assumed that was because it was all broken up inside, but you know what happens when you assume...

No more rattle!

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Unread 09-18-2013, 08:23 AM   #17
V65Ozzie
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Join Date: Feb 2012
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Quote:
Originally Posted by Kingr98 View Post
It seems a little off topic at this point, but my cat problem has been solved.

I took it to a local muffler shop and 30 minutes later, i gave the guy $30. As riot1987 said, he used a sawzall to cut the old one off, and as pageman said, he welded the new cat on.

I could definitly see light through the new cat, but only darkness through the old. I assumed that was because it was all broken up inside, but you know what happens when you assume...

No more rattle!
If it rattled, it was broken. It could also have a melted substrate(raw fuel in the exhaust system pools in the converter and eventually lights off) or it could be sooted up. I've replaced literally thousands of cats over the years( I worked in the exhaust business), the vast majority can be done in 30 minutes or less, there are others that can take a few hours. I have a sawzall, a welder and oxy-acetyline at the house, I do my own. When I have to do my ZJ, it will get a true high flow cat, basically it will be a gutted body with an emulator plugged in behind................did I say that out loud? Feds, please disregard the previous statement. These are not the droids you are looking for.
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Unread 09-18-2013, 08:49 AM   #18
zjosh93
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I always thought that the "high flow" thinking was more related to replacing old style pellet substrate cats with modern honeycomb versions, not replacing this honeycomb with that honeycomb. I remember magazine articles from the mid 90s about swapping those big old cats for the honeycomb cats and picking up decent power. I also read an article in one of the Ford magazines in the mid 2000s where they tested stock cats, aftermarket cats, someone's "racing" cats, and straight pipe on a 600 hp supercharged mustang. Must've been 04 or 05 since I think it was one of the supercharged Cobras. The conclusion was that you lose few enough hp to a good cat that the straight pipe isn't worth the risk. Don't get me to lying but I think the straight pipe, racing cat, and aftermarket cat were within 20 hp, so about 3%, or 5 hp on a 4.0. Seems about right.
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Unread 09-18-2013, 09:17 AM   #19
PolkaPower
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Quote:
Originally Posted by zjosh93 View Post
I always thought that the "high flow" thinking was more related to replacing old style pellet substrate cats with modern honeycomb versions, not replacing this honeycomb with that honeycomb. I remember magazine articles from the mid 90s about swapping those big old cats for the honeycomb cats and picking up decent power. I also read an article in one of the Ford magazines in the mid 2000s where they tested stock cats, aftermarket cats, someone's "racing" cats, and straight pipe on a 600 hp supercharged mustang. Must've been 04 or 05 since I think it was one of the supercharged Cobras. The conclusion was that you lose few enough hp to a good cat that the straight pipe isn't worth the risk. Don't get me to lying but I think the straight pipe, racing cat, and aftermarket cat were within 20 hp, so about 3%, or 5 hp on a 4.0. Seems about right.
It's just that the OEM cats have more catalyst in them and don't flow as freely as the Magnaflow or other high flow cats which have less catalyst. Kind of like the K&N has less filtering and flows better because of the wider holes than the stock paper which filters better but is more restrictive.
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Unread 09-18-2013, 11:58 AM   #20
Marcos
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Originally Posted by JeepNicholson View Post
That article isn't entirely correct. Some use a ceramic honeycomb substrate, and some use a metal foil substrate. The metal foil can have larger passages, but the same # of cells and total catalyst surface area, because the wall thickness is less.

My '93 came with a ceramic substrate OEM cat which I recently replaced with (what I was told was) an OEM replacement cat with a metal-foil substrate. The original was oval in cross section, the replacement was circular.
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Unread 09-18-2013, 12:35 PM   #21
Kolak
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Many factors come into play to influence converter flow:

The size of the substrate
The shape of the substrate
The number of perforations in the substrate
The size and shape of the case
The frontal area dimensions of the case
The shape of the transition from the pipe nipples to the case

Certain, but not all, Magnaflow converters are optimized to be high flow. These units not only flow extremely well, but test clean and are very affordable.
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Unread 09-18-2013, 05:16 PM   #22
pageman
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lets put thing in this view.
1. you need cats to be legal so if its got a plate you need it(not matter how much gains if you got rid of it)
2. factory cat is designed for epa emissions and noise control and cheapness
3. a high flow cat cost a little more and is designed to function in accordance to epa just in a losser sence but still bound in the law thats how they can out flow factory cats yet still be leagl.
4. high flow cat companys NEVER claim to make more power than straigh pipes. in motor dynamics this has been proven restriction=less power and econ but = leagley driving on the road
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Unread 09-18-2013, 05:26 PM   #23
coralman
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Dagnabbit,lol, now I am more uncertain than ever. I was going to do the wj manfold swap, 703's, apn header and a magnaflow catback. Piece by piece that plan has been cast into uncertain realms.

Wj swap- some say that it improves things, not drastically,unless you port the manifold and make other modifications. The basic net gain was a change in the torque curve. I've lost track whether is was on the low or high end. Plus some had clearancing issues on the manifold itself, others issues with manifold vacumn that really never get solved.

703 injectors- General consensus of a smoother idle, not much else, which you could probaly aquire with a rebuilt or new set of the standard siemens injector. The bosch models by word of mouth are not as prone to stick or leak. Better diffusional spray which for some results in cleaner quicker starts. But also reports of running too rich at higher rpms, by testament of the rotten eggs smell.

Apn header- In combination with a smoother intake of air from the wj manifold this gives a more efficient exit of exhaust. Newfie says the better idea from there back is to increase the pipe size going into the cat.I can go with that but in my case no shop in this town is willing to build a custom front pipe. So I'm stuck with a new mopar front pipe of OE configuration. Some adapting would be in order, minimal, to get the front pipe to the cat. So to summarize, I'm bringing air in more smoothly but not necessarily more air because that is limited by the throttle body bore. I would have a more efficient injector but at higher rpms may run too rich which in turn screw up the new cat possibly. The header will allow a freer breathing motor to a point, but may be negated by the OE chokepoint.

Magnaflow catback- The muffler tailpipe looks to be of good quality. I don't want alot of racket since I'm passed the stage of vroom vroom and listening to YouTube clips I like the sound. I want the stainless as well. Not aluminized steel. Problem is they stop the listing at 97. Magnaflow has no idea if it will fit a 98 but was told" it probaly would" by a grouchy dude on mags payroll.

High flow cats- Thanks for the lesson newfie. Other concerns are the 2nd O2 with reports of them setting off codes. Having to move the 02 out of the exhaust flow using spark plug adapters or inline chips to give the O2 proper reads. The OE O2 circuit/pcm is geared to look for a certain value. If gas is moving faster, would not the catalyst have to be more efficient to give the required value with less catalyst? Magnaflow offers "heavy metal cats" which I assume means more of the materials for conversion instead of a ceramic "stage" coated with the metals. I guess I don't have a grasp of this stuff as well as I thought I did and at this point am just teetering on putting the crap back like it was from the 98 zj inception.

There are so many variables when reading stuff online. The guy that had to move the O2 may have had a leaky injector to start with, you just don't know. The vacumn problems may be a faulty gasket, a minute break in a hose, a port, a warped manifold. Apn is not a top quality header and may have fitment issues, and in reality may crack just like the original because of flaws in the lack of a split 3 and 3 configuration over the inline welding of six tubes. Its just alot to digest and I have spent a year observing jeepsters in this and other forums making these mods and I'm not a ding dang bit closer to making up my mind,lol. Sorry for the rant, I get frustrated sometimes.
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Unread 09-18-2013, 06:22 PM   #24
pageman
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yes it can all be confusing.be sure of this by replacing OE cats and mufflers whith high flow street units will help. now this will not be a HUGE upgrade. its not like a super charger or light weight internals now it will help alot combine this whith a quality intake and headers whith matching pipe diameter then a further step up is bigger valves/hot cams along with port and polishing the heads and intake
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