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Question for the exhaust gurus.....

B

Ben824

NAXJA Forum User
Location
Woodstock, GA
Ok so I have been running my custom dual exhaust set-up on my 97 4.0L auto 4x4 for about 4 years now and it consists of a Banks header, stock down pipe, heddman 3" in/out high flow cat, flowmaster 50 series 3" in/ 2.5" dual out, 2" pipes goin back to 2.5" tips. The muffler I changed almost 2 years ago from same set-up but gibson flow through because I heard an XJ with the flowmaster 50 series and I liked it's sound better. I know some modern day EFI cars if not tuned after an exhaust upgrade can actually be hurt by too much free flowing exhuast rather than helped. With my exaust pipes being so big (i.e. cat and muffler) am I doin more harm than good? I know the dual exhaust serves no benefit I just like the look of 2 REAL pipes and wanted to be unique and different. Well I've started to hear a familiar rattle from the exhaust from the cat area so I took it to a exhaust shop for a professional opinion and sure enough he confirmed it that the cat is goin bad. The Check Engine Light hasn't come on yet but the rattle is driving me crazy and sounds like sh*t. Anyway my question is should I try goin with a small in/out when I get a new cat maybe a 2.5" in/out? Also I thought this cat would have lasted longer than 4 years, anyone have a suggestion on a longer lastng high performance cat? I have heard magniflow alot but I didn't know if that was just becasue they were the cheapest or something. Stock converters are too much money and I know they will go bad again mine went out around 6 years old. Anyway thanks for any help. Oh I can't go changing the whole exhasut around again so any radical change suggestions won't be helpful I am mainly asking about the cat.
 
sounds like you have dual tailpipes, not dual exhaust.

one option would be to gut the cat, but thats technically illegal.

ebay has cat convertors for cheap or go to the local auto parts store and get a universal cat. i would stick with a 2.5 diameter cat.
 
Where I am from "dual exhaust" means dual tailpipes and "true dual" means a true dual exhaust coming from each side of the engine which would be kinda hard on a inline 6 lol but yah I hear what ya mean thats just how we refer to it around here. I was just trying to see what some people thought about whether or not I had too much free flow exhaust from the bigger diameter cat and if I knocked it down some if maybe it would give just enough extra backpressure to help things out. The engine feels strong and runs fine but my gas mileage kinda sucks and I have done every tune up maintenance possible and had the whole BG engine, intake, and fuel system cleaner run through it at a shop and he said the Jeep didn't really need it that it wasn't that dirty. Like I said in the first post I had heard that too much free flow on modern day EFI can actually hurt power and mileage rather than help it since its too far out of the factory tuning. I though about just goin back to a stock cat but a local shop said that would be $400 which I can't afford on a college budget but he said he could do me a magniflow for $225 which I might be able to do and I was affraid that a stock cat may add more back pressure than I would want and possibly quiet my exhaust down more than I would want also. Anyway thanks for the opinion and if anyone else has one feel free to add.
 
You can get those magnaflow cats for under $90 if you or someone you know is up to the task.
 
man, your posts are long winded. cat laws vary from state to state. i run no cat here in FL. removed the cat and went with a piece pf 2.5" straight pipe. i get compliments on how it sounds with an APN header stock down pipe with the stock "dent" hammered out. flowmaster 40 and 2.5" out to the tip. tip is 3" for an echo can type effect that is an old hot rodder trick i learned.

what are the emissions laws in GA?

$90 for a high flow or $5 for a piece of straight pipe. take your pick if you can get away with it. you could always replace the cat when you need to get the emissions tested if necessary.
 
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Emissions laws in GA require any vehicle registered in the state to have a catalytic converter and if you live in the metro Atlanta area you must have an emissions test once a year when you renew your tag which my Jeep is still under my Dad's name (I am a college student) and he still lives in the Atlanta area so it still needs a cat. And sorry for the long posts just wanted to make sure anyone that read it knew the full story and could give me the most accurate advice. I know I can get a magniflow 2.5" in/out from summit racing for like $69 I think so I'm gonna call that shop back tomorrow and see how much they would charge just to put it on for me.
 
tigerShark said:
man, your posts are long winded. cat laws vary from state to state. i run no cat here in FL. removed the cat and went with a piece pf 2.5" straight pipe. i get compliments on how it sounds with an APN header stock down pipe with the stock "dent" hammered out. flowmaster 40 and 2.5" out to the tip. tip is 3" for an echo can type effect that is an old hot rodder trick i learned.

what are the emissions laws in GA?

$90 for a high flow or $5 for a piece of straight pipe. take your pick if you can get away with it. you could always replace the cat when you need to get the emissions tested if necessary.
Click to expand...

Just because you have no CAT doesn't mean it is legal. Your setup is absolutely illegal in FL, they just don't check.

It is also stupid and irresponsible. With all of the bad press the 4x4 community gets in general we need to make sure our vehicles are as clean running as possible. Not to mention I like breathing and don't really want to were a gas mask every where I go.


BACK ON TOPIC!

As far as your question on the whether 3" exhaust is a hindirance I can't say. Someone with a better knowledge of the 4.0 would have to answer that.

If your CAT is going bad the magnaflow is probably your best bet. There are more expensive CATs that are stainless but from my experience they are not constructed any better. (I.E. the rattle you have). It is an unfortunate reality that most products are poorly constructed. Even if you buy a "factory" style CAT it may or may not last like the original.
 
Well the factory one sucked and crapped out after 6 years and this one crapped out after 4 so I guess that all Im gonna get out of these things but for the price of the magniflow I will settle for another 4 years instead of dropping $400 to only get another 2 years out of it.
 
Ben824 said:
Ok so I have been running my custom dual exhaust set-up on my 97 4.0L auto 4x4 for about 4 years now and it consists of a Banks header, stock down pipe, heddman 3" in/out high flow cat, flowmaster 50 series 3" in/ 2.5" dual out, 2" pipes goin back to 2.5" tips. The muffler I changed almost 2 years ago from same set-up but gibson flow through because I heard an XJ with the flowmaster 50 series and I liked it's sound better. I know some modern day EFI cars if not tuned after an exhaust upgrade can actually be hurt by too much free flowing exhuast rather than helped. With my exaust pipes being so big (i.e. cat and muffler) am I doin more harm than good? I know the dual exhaust serves no benefit I just like the look of 2 REAL pipes and wanted to be unique and different. Well I've started to hear a familiar rattle from the exhaust from the cat area so I took it to a exhaust shop for a professional opinion and sure enough he confirmed it that the cat is goin bad. The Check Engine Light hasn't come on yet but the rattle is driving me crazy and sounds like sh*t. Anyway my question is should I try goin with a small in/out when I get a new cat maybe a 2.5" in/out? Also I thought this cat would have lasted longer than 4 years, anyone have a suggestion on a longer lastng high performance cat? I have heard magniflow alot but I didn't know if that was just becasue they were the cheapest or something. Stock converters are too much money and I know they will go bad again mine went out around 6 years old. Anyway thanks for any help. Oh I can't go changing the whole exhasut around again so any radical change suggestions won't be helpful I am mainly asking about the cat.
Click to expand...

Getting back to your original question: I have a similar exhaust setup on my 91 MJ w. a Hesco 4.5L stroker. Mike Leach headers into a 2.5" in/out cherry bomb in place of the cat (no emissions testing in AL), and a Walker hi-flow muffler w. single 2.5" in with dual 2.5" outlets, and dual tailpipes exiting under the rear bumper. I tried a Flowmaster 40 series but it was too damn loud and droned badly at 2100 RPM or so. I did have dyno runs before and after the exhaust mod and picked up roughly 10% on the peak torque and HP readings at slightly higher RPMs. The before exhaust was basically stock w. cat except for the same headers. I think the 2.5" pipes all the way through were ideal for my setup.
 
DaJudge said:
Just because you have no CAT doesn't mean it is legal. Your setup is absolutely illegal in FL, they just don't check.

It is also stupid and irresponsible. With all of the bad press the 4x4 community gets in general we need to make sure our vehicles are as clean running as possible. Not to mention I like breathing and don't really want to were a gas mask every where I go.
Click to expand...

Here we go again another tree hugger. Every time someone even remotely mentions not running a cat somebody has to go off and get their panties in a bunch. I personally am tired of reading exhaust threads where people are seeking out assistance in making a decision regarding whether they should waste more money on an aftermarket cat. Then someone jumps in and tells them how they should build their rig and if not done the way they believe they get criticized and called "irresponsible". I'm sure the OP has a pretty good idea whether or not he should run a cat. Obviously if he doesn't he gonna have an ses light on unless he buys an o2 sim or has it specifically deleted out of the computer. Also if Tigershark doesn't want to run a cat let him. I can guarantee you just because you said it irresponsible he's not going to go out and purchase two brand cats and install them on his rigs just because your panties are in a bunch and think we're all gonna die because "we're" depleting the ozone. They way I see it we went through an ice age and who's to say we're not going to go the some sort of warming period? Also have you ever thought that maybe this is just the way the ozone is? We haven't had the technology around long enough to even know how the ozone changes over a several hundred year period. Leave those who don't run cats alone and keep your ever so exacerbated opinions to yourself.


Sorry from taking away from the OP.
 
X2 :yelclap:

exhaust2.jpg
 
To make sure everyone understands, I know that running no cat can be better for power or sound or whatever but I'm trying to do what is best within the factory tuning to ensure good power but also good economy and like I said in the OP I had HEARD that TOO much flow on a modern day EFI could throw it off and actually hurt it more than help so I figured I would find someone with more knowledge/experience to help answer my question. I dont give a sh*t if you run a cat or not I think the whole "global warming" myth is a liberal media created hype however I do believe in environment global warming (yes there is a difference and if you don't think so I dare you to google it right now) but that is a completely different discussion not relevent or appropriate for this thread. I am only going to run another cat because my Jeep is in my Father's name still, and if I try to take it off and "trick" the government my Dad would kick my a** for getting him in trouble if I got caught. And to reiterate, cars registered in the Metro Atlanta area are required to have an annual emmisions test performed to renew the tag and it will not pass on OBDII cars with a Check Engine Light on or older cars with the cat removed. So guys lets do our best to stay on topic here. Thanks again to those that are trying to help out a fellow Jeeper.
 
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