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i want to take out last cat's in each exhaust line on my mustang. its pretty much a stock GT mustang with 2 flowmaster 40's that drop off before the axle.i was wondering if there are going to be any problems after i take them out. like future smog ploblems and stuff like that. any ideas?
 

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You can remove any of the cats that are located behind the rear-most o2 sensor and not have any problems. Once you remove cats that are in front of the o2 sensors, you will begin to throw check engine codes.
 

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You can remove any of the cats that are located behind the rear-most o2 sensor and not have any problems. Once you remove cats that are in front of the o2 sensors, you will begin to throw check engine codes.
True that, BUT if you want to take em all out witch is the best way:) you can get MIL eliminators, witch will prevent you from seeing check engine lights. They go inplace of the O2 sensors and can be found at

Mustang Parts & Performance - American Muscle
 

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Just wondering if everyone is aware there is a difference between the front and rear cats. The front cats are called "light off" cats. The real work is done in the rear cats.

Sooooo if you take off the front cats, then the un-burnt fuel that would have been burned in the light off cat now goes straight to the rear cat. The excessive fuel will make the cat run hotter and decrease it's service life.

The car will likely pass inspection at first, but don't expect the remaining rear cat to last as long.
 

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I'm new to modding aswell.. Is there a way to remove all cats and still pass inspection? I wanted to go the bassani xpipe and borla stinger approach.. If I cant pass inspections with full straight pipes what do i need to make it just enough to pass
 

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I'm new to modding aswell.. Is there a way to remove all cats and still pass inspection? I wanted to go the bassani xpipe and borla stinger approach.. If I cant pass inspections with full straight pipes what do i need to make it just enough to pass
If your state does a visual inspection, you're ******.
I've heard of people passing emissions with no cats and a good tune.

Your best bet is to run whatever mid-pipe you want, and hang onto your OEM pipe and swap it for inspections.
 

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I live in Texas and I've never had a guy check under the car.. Hell some of them never even popped the hood. Haha the last guy I went to notice I had his shops oil change sticker.. He was like "I see your a returning customer.. I'll give you the 'special' inspection.." The intake on my Celica kept setting my MAF sensor off and he ignored it :D
 

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i want to take out last cat's in each exhaust line on my mustang. its pretty much a stock GT mustang with 2 flowmaster 40's that drop off before the axle.i was wondering if there are going to be any problems after i take them out. like future smog ploblems and stuff like that. any ideas?
I didn't really bother with reading all of the responses before coming to my own conclusion on this. Besides, a couple of the responses were just fundamentally way off on at least a point or two.

Here's your answer, and I promise it to be absolute truth. DO NOT make any permanent changes to your factory catalytic converter pipe. Cutting out cats and replacing them with a section of straight pipe would be considered a "permanent change". You WILL NOT pass smog (sniffer), and you WILL NOT pass visual. Anyone who is aware of the existence of the State of California in and of itself should realize that California not only has the strictest laws when it comes to this subject, but we also set the bar for the rest of the country.

Now for your options...

1) Do nothing.
2) Off-Road or catted aftermarket midpipe.

I personally don't like Option 1, so what I do is run an o/r midpipe and put my factory catted pipe back on every other year for a little while so I can go do my smog test. "But why not a catted midpipe?", some may ask. Aftermarket catted pipes only come with two cats, whereas the factory supplied pipe has four (2001-04) or six (1996-00) cats. Quite likely won't pass sniffer (think about it, how could two 'high flow' cats do the same job as four restrictive ones?), and definitely not visual, so don't waste the money on one, imo. The State of California is looking for stock oem components in stock locations. This is why you can't have longtube headers here in CA, as installing them requires relocating the converters.
 

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I would suggest for you to run this off-road x-pipe until it's time for your test, and then I'd reinstall the factory pipe.

99-03 Mustang Off Road X Pipe
 

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do you care about the air people breathe and the work LA has done to clean up the smog there? Be responsible and get some hi flow cats...to run without them is not only illegal, but immature.
 

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do you care about the air people breathe and the work LA has done to clean up the smog there? Be responsible and get some hi flow cats...to run without them is not only illegal, but immature.
The point I was attempting to make in my earlier post is that it's illegal anyway. You can spend $450 on a catted midpipe or $150 on an off road pipe, but the only difference between the two is $300. Neither of the two will be remotely close to compliant. So by my own logic one might as well save $300. Or just say fcuk it altogether, leave the factory midpipe in place and look for performance gains elsewhere.

I generally enjoy your posts and find them informative, but by your logic in reference to the use of the word "immature", does that also extend to those who on occasion operate an older car that has no pollution controls installed? How about motorcycles? Haven't seen too many Harley's with catalytic convertors. Besides model year, in practical application what's the difference? Both of my cars are emitting hydrocarbon emissions that are beyond any current legal standard of allowables, with the only difference between the two being that one is legally allowed to. I suppose you could more justifyably call it "irresponsible", but then by that logic I suppose all cars built pre-1974 should be dismantled and crushed. I think I understand where you're coming from, which is something to the effect that environmentally speaking, we shouldn't be just completely shitting all over everything. And to a good point I tend to agree. But if anybody's asking me to feel guilty for removing some of the pollution control devices on my car then I hope they're sitting down and prepared for a disappointing response. In regard to air quality issues facing the greater Los Angeles area, for those of us who remember what it looked like in the 1970's (I was a little young, but I've seen the pictures and heard the stories) then yes, air quality has been vastly increased due in no small part to regulations imposed upon the automotive industry. But another huge part, really the key to these improvements has been changes made within the manufacturing/industrial sector. It's a poor argument to persue, but something else to be considered when discussing a city like Los Angeles is, it will always be a dirty nasty place to live. All the Prius' and Chevy Volt's in the world ain't gonna fix that.

/incoherent rambling and ranting.
 

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Discussion Starter #12
hey thanks for all the help. i thinkim going to go for that UPR X pipe. and i called every local muffler shop and they said they wont even touch the cats, unless its to replace them. i even lied to them and told them it was a race car. and one guy said if i trailer it over there and prove that its not insured for street use, he might take a look at it hahah. stupid smog laws.
 

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hey thanks for all the help. i thinkim going to go for that UPR X pipe. and i called every local muffler shop and they said they wont even touch the cats, unless its to replace them. i even lied to them and told them it was a race car. and one guy said if i trailer it over there and prove that its not insured for street use, he might take a look at it hahah. stupid smog laws.
If you can't do it yourself (it's pretty easy, requires minimal tools, and can be done in about an hour) then find a "mom n' pop" shop. Big shops, or those with a smog testing license to protect won't touch it. There's too many stories out there about undercover "sting" operations to catch shops or their tech's looking the other way that just makes it too risky for them to do it any way but by the book. Little mom n' pop garages generally don't care though.
 

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It's a poor argument to persue, but something else to be considered when discussing a city like Los Angeles is, it will always be a dirty nasty place to live. All the Prius' and Chevy Volt's in the world ain't gonna fix that.

/incoherent rambling and ranting.
Yep....it can get pretty nasty, about the only thing that will clear up all that sh!t is to blow out a few of those mountains and let the pollution move out.

The true origin of air pollution in California dates way the he!! back....much further back than anybody's car giving an effect on it.

Don't get me wrong.....millions of cars certainly didn't help the matter at all and with the newer emission controls put into effect for the LA area...it has helped, but.....the smog and pollution is a side effect of the areas general layout......

Nice little history........

50th Anniversary of Smog War
 

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do you care about the air people breathe and the work LA has done to clean up the smog there? Be responsible and get some hi flow cats...to run without them is not only illegal, but immature.
The point I was attempting to make in my earlier post is that it's illegal anyway. You can spend $450 on a catted midpipe or $150 on an off road pipe, but the only difference between the two is $300. Neither of the two will be remotely close to compliant. So by my own logic one might as well save $300. Or just say fcuk it altogether, leave the factory midpipe in place and look for performance gains elsewhere.

I generally enjoy your posts and find them informative, but by your logic in reference to the use of the word "immature", does that also extend to those who on occasion operate an older car that has no pollution controls installed? How about motorcycles? Haven't seen too many Harley's with catalytic convertors. Besides model year, in practical application what's the difference? Both of my cars are emitting hydrocarbon emissions that are beyond any current legal standard of allowables, with the only difference between the two being that one is legally allowed to. I suppose you could more justifyably call it "irresponsible", but then by that logic I suppose all cars built pre-1974 should be dismantled and crushed. I think I understand where you're coming from, which is something to the effect that environmentally speaking, we shouldn't be just completely shitting all over everything. And to a good point I tend to agree. But if anybody's asking me to feel guilty for removing some of the pollution control devices on my car then I hope they're sitting down and prepared for a disappointing response. In regard to air quality issues facing the greater Los Angeles area, for those of us who remember what it looked like in the 1970's (I was a little young, but I've seen the pictures and heard the stories) then yes, air quality has been vastly increased due in no small part to regulations imposed upon the automotive industry. But another huge part, really the key to these improvements has been changes made within the manufacturing/industrial sector. It's a poor argument to persue, but something else to be considered when discussing a city like Los Angeles is, it will always be a dirty nasty place to live. All the Prius' and Chevy Volt's in the world ain't gonna fix that.

/incoherent rambling and ranting.
Yep....it can get pretty nasty, about the only thing that will clear up all that sh!t is to blow out a few of those mountains and let the pollution move out.

The true origin of air pollution in California dates way the he!! back....much further back than anybody's car giving an effect on it.

Don't get me wrong.....millions of cars certainly didn't help the matter at all and with the newer emission controls put into effect for the LA area...it has helped, but.....the smog and pollution is a side effect of the areas general layout......

Nice little history........

50th Anniversary of Smog War
Wow...
This went from catted/catless midpipes to an environmental cleanliness debate?
:hijacked:
 

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Wow...
This went from catted/catless midpipes to an environmental cleanliness debate?
:hijacked:
Yeah despite everyone's best intentions it still went downhill, lol:run_over:
 

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hey thanks for all the help. i thinkim going to go for that UPR X pipe. and i called every local muffler shop and they said they wont even touch the cats, unless its to replace them. i even lied to them and told them it was a race car. and one guy said if i trailer it over there and prove that its not insured for street use, he might take a look at it hahah. stupid smog laws.
Sounds good man. Two things to tell you.

1. you'll get a check engine light if you don't use MIL eliminators on your rear O2 sensors (they're cheap) or use your tuner to turn off the rear O2 sensors. If you don't have either of these, we can hook you up with either one at UPR Products.

2. AFM members get a 10% discount on our webstore. Send me a PM before you order and I'll give you the discount code. :bigthumbsup
 

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Discussion Starter #18
my father has a 1969 boss 302 mustang and he has 2 lobak mufflers on them that are about 30 years old. i currently have a 2003 mustang gt with 2 flomaster 40's. i was wondering if anybody knew anything about lobaks and weather or not they would sound good on my car. my father said he would trade me for my flowmasters. any ideas?
 

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Holy Sh!t. I am really sorry guys, i had no idea the pain you go thru with this law..... Anyways, thanks, now i can put a name with a face on that freaky factory pipe with the 6x cats thats sitting in the junk pile. :winks
 

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Hey guys sorry to resurrect this thread but I was wondering if getting high flow cats will allow me to pass inspection both state and smog smog. I just bought a 2002 Mustang GT with an entire aftermarket exhaust thank you
 
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