Removing the cat

Unforunatly, I dont have the money for cat back exhaust but i was wondering if any1 had experience with removing the cat on an 04 gt and putting mufflers on? bad idea?? any feedback will help thanks

If you're talking about removing the catalytic converter and not replacing it be aware that it is a violation of federal law. In fact The Clean Air Act of 1990 has amendments which prohibit private individuals from removing them from their vehicles.

Thanks for pointing that out Tom but we will allow discussions concerning the pros and cons of doing so in this specific forum regardless of the legality. It has been awhile since we had a removal of CAT convertor discussion. Our job is to keep it fair and balanced and not discourage members but point out the possible ramifications or benefits. I thought Illinois was a green state and has it's own version of the EPA so that state's rules are applicable too. They mandate a similar odb-ii emissions test like Texas for '96 and up cars. No more tailpipe exhaust sniffer. See link below.

Click here (http://www.epa.state.il.us/air/vim/faq/obdlong.html)

Many of us race our Grand Prixs, especially members with modded GTPs and removal or bypass of the CAT convertor for off-road racing purposes only is OK and not illegal. For general street use and daily drivers it doesn't make sense to remove the CAT. Also, with a GT model I dont see any benefit if it is not modded in other areas. You will get an odb-ii emissions fault once the rear 02 sensor detects CAT removal or no change between the front and rear 02 sensor signals. However, there are ways around that with an 02 simulator and/or re-programming the PCM module to inhibit any DTC like P0420, etc. but allow all emissions readiness indicators to set properly and give no SES/CEL Mil light. My Intense PCM is programmed that way. However, I pass Texas emissions odb-ii testing with flying colors. :grinyes:

Also, you can run an aftermarket exhaust cutout device that keeps the exhaust stock with CAT convertor intact but opens the exhaust up and bypasses for off-road racing purposes like at the dragstrip but rather noisy though.

CATBack exhaust systems are great for sound but do little in hp or any significant performance gain. Especially when you consider the cost.

I think he thinks the cat back systems remove the cat. But they start after the cat. just my :2cents:

I think he thinks the cat back systems remove the cat. But they start after the cat. just my :2cents:
That's what i thought as well and posted about the federal law. It amazes me that after so many years and advertising about the law and numerous PSAs, people don't realize in most cases cannot ask a shop to remove the cat or do it themselves. Every once in awhile we'd have someone come into the shop inquiring if we could remove their cat for various reasons. And a couple of weeks ago I was talking with a friend who is a manager with an auto parts store and the discussion was auto related (of course:lol:) and the subject of exhaust systems came up. He even mentioned that he is amazed at how many people still come into the store looking for straight pipe or other means to rid themselves of their catylitic converters.
A few months ago in our local paper was an article about a sting operation put on by various agencies and the police. They targeted different shops, including muffler shops to see who was following the law. They found a few people breaking the law by illegally removing cats from vehicles . They found a few shops who broke the law,(including one exhaust shop) and two individuals doing work privately out of their home garages. I don't recall if the people in question were arrested, bu ti remember the article saying they faced heavy fines.

thanks guys for ur advice i really appreciate it, i just needed to no cuz i was considering getting a pcm but one of the requirements is having cat back exhaust and I was thinking of getting rid of the cat an throwing flowmaster mufflers on. I highly doubt i will remove it cuz it is only a daily driver. thanks again

There is no requirement to use a CATBack exhaust on a GT or GTP with a re-programmed PCM module from Intense, DHP or ZZPerformance. As I mentioned earlier a CatBack exhaust is a waste of money due to the cost per horsepower. Now you will need to use premium gas with the re-programmed PCM.

And don't let the replies discourage you from modding your GT. There are alternatives and many use theirs as daily drivers with exhaust mods. I recommend leaving the CAT intact but use a Hi-Flow CAT such as a Magnaflow with at least 2.5" inlets/outlets. You can get rid of the u-bend and delete the resonator. Then go with the Flowmaster mufflers or other aftermarket mufflers.. Also, you could use a 2.5 or 3.0" downpipe and go to custom plumbing greater than the stock 2.25" at least to the output of the mufflers.

thanks for the info on the pcm but i was just a little confused from what pfyc.com had on their pcm here check it out....http://www.pfyc.com/pc/GP3901/04UNDER/Digital+Horsepower+PCM+-+2004%2B+Grand+Prix.html


The input on the exhaust is well appreciated i didnt no that could work, im still kinda new with this so any info will help.....on 3800.com the downpipe and high flow cat come together if u pay a lil extra and it deletes the u-bend so thats a plus. I'm not sure what the resonator is or what it does??

I'm not sure what the resonator is or what it does??

All the resonator does is help illiminate noise from resonant or secondary frequencies which can be annoying at times like on a long trip. Other than that it can be removed. It is the tubular looking part like a muffler you see after the CAT convertor but before the mufflers. I have mine deleted. The noise level will be a little higher.