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high flow cat or no cat?

I

irish636

NAXJA Forum User
Location
louisville, ky
i just put a flowmaster 40 on my 99 yesterday. i like the sound but i wish it was a little louder when i got on it. i was thinking a high flow cat or maybe even no cat. i dont want it to be loud as hell and i dont want it to pop. what should i do? thanks guys!
 
what size is your piping?

i had mine done yesterday as well, with a new high-flow 2.5" cat, 2.5" FM40, and 2.5" piping out to the back...they tapered it down to 2.25" at the end of the tailpipe to fit thru the opening in the back, and it still seems plenty loud.

rhino317 said:
what year is your xj
Click to expand...

you're not really asking that are you?
 
You're better off using a cat. Modern cell-based cats don't have the same kind of airflow restriction problems that old-style pellet-based designs had, and in some cases running without a cat will just introduce more problems.
 
WheelinJR said:
what size is your piping?

i had mine done yesterday as well, with a new high-flow 2.5" cat, 2.5" FM40, and 2.5" piping out to the back...they tapered it down to 2.25" at the end of the tailpipe to fit thru the opening in the back, and it still seems plenty loud.



you're not really asking that are you?
Click to expand...




yah i did until i read back in it, then i edited it so i didnt think it would show up.
 
just run it without any cat or muffler. that's what i'm doing at the moment. i went from the stock 2.25" cat to a 2.5" FM40 and 2.5" piping all the way back. it was hacked pretty bad so i'm going back and fixing all my mistakes. when i took the muffler off i realized that the cat was rotted out inside so i just decided to rip that off too. i'm waiting to buy a new one to put everything back on, but it sounds pretty nice with a straight pipe outta the headers. btw, mines a 94 so i don't have the o2 sensor problem.
 
i only have the stock piping right now. i want to put the money towards other things on my jeep so i just put a muffler on. would a high flow cat make a bid difference? thanks for all the info guys
 
here we go again. for future reference, a search on this subject will bring up alot of debate.

run the cat. don't give the greenies another reason to hate us. they're not that expensive, and a new stock replacement cat will already make you happy with the power you get back compared to an old clogged one.
 
I have my cat hollowed out. It sounds nice, but other than that i really don't see a need for it. I have the stock muffler on there still, and with the cat the way it is, it sounds like i have a nice quiet aftermarket exhaust. like I said though, really not worth it, as i can't feel any performance gain at all and have had my CEL come on and off intermittently since doing that. It did pass smog though :)

The environment point is a good one. I've been meaning to go get a new cat, but haven't had the cash.

If i could do it over, i probably wouldn't have messed with it. making car alarms go off in the parking garages is funny, but that same tone gets annoying sometimes when you don't want to be loud, or on long drives on the highway.
 
Just be aware, it's illegal for a shop to remove a cat from a system that already has one and in many states, it won't pass inspection without a cat.
 
leave the cat on. its not worth taking it off. oNe its illegal and two they really do help keep the emissions down. And yes all your o2 sensors past that will be wrecked really soon. :peace:

(play nice... -Mod.)
 
Last edited by a moderator:
Not running cats gives the green people even more of a reason to keep taking our wheeling spots away from us. Leave cats on. It isn't worth removing just for a damn sound.
 
88XjLaredo said:
Not running cats gives the green people even more of a reason to keep taking our wheeling spots away from us. Leave cats on. It isn't worth removing just for a damn sound.
Click to expand...

YES!

A catalytic convertor should be required to have a NAXJA membership too. Hasta
 
WheelinJR said:
YES!

A catalytic convertor should be required to have a NAXJA membership too. Hasta
Click to expand...

Running a cat should be one of the "True XJ" requirements.
 
I'm not going to argue about the enviromental, in many cases you can pass an emissions test without a cat, IF the motor is in good condition. Modern computer systems have tight control over the motor and can do a pritty good job on their own.

BUT as has been already pointed out it is illegal to remove the cat and in most cases will not help the performance and in the case of newer motors, OBDII, it will actually run worse.

I just got done putting a cat on my 97 wrangler, the previous owner removed the cat and put a flowmaster 40 series on. It was loud and sounded like crap (4 cyl) and the check engine light would come on every couple days.

The worst part was the engine was in open loop all the time and sometimes would not idle or accelerate. I would have to stop and le the computer do its thing before it would idle correctly.

By the time I got a cat put on it had destroyed the down stream O2 sensor so i had to replace that as well. Now with the cat and the 40 series it sounds diecent, a little louder then most but not the honda fart tube sound it had before, and my fuel economy went up.
 
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