Gutting/removing catalytic converter [Archive] - GrandAmGT.com Forum

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03Grandam
03-04-2009, 12:13 PM
I was thinking of taking my cat off and gutting it and then putting the pipe back up so it looks stock.



My question is this, is there anyone of does anyone know of someone who took their cat off. I'm curious to know if my check engine light is going to come on and any other problems that I may incur.


I want a better sounding exhaust and a little more acceleration out of it, I dont want to take the stock exhaust off either. I dont want those ****ty sounding after market exhaust that are loud as hell.

timka86
03-04-2009, 12:19 PM
gutting/removing cat will make your car louder, the stock cat also acts as a reconator, you will for sure get a check engine light, as the O2 sensor post the cat will be receiving incorrect readings. you will not pass emissions unless other modifications are done. (i don't know if MI has emissions testing)

03Grandam
03-04-2009, 12:25 PM
No, we dont have testing. What if I remove the resonator, do you think that would cause my check engine light to come on?

Would that increase the the sound of my exhaust?

SSRacer
03-04-2009, 12:31 PM
Removing the resonator will not cause any codes as it is past all the sensors.

timka86
03-04-2009, 12:37 PM
as mentioned above removing resonator wont cause codes, it will make exhaust louder. (not as much as removing the cat will)

03Grandam
03-04-2009, 12:38 PM
Alright, but how about a little bit louder of an exhaust?

Think it might also increase exhaust flow and give me slightly more acceleration??

I don't give a crap about top end power.

03Grandam
03-04-2009, 12:44 PM
Never mind, I totally didnt even see what you said above in my last post.

Sorry.

timka86
03-04-2009, 01:05 PM
The biggest bother to me was the drone you get at cruising speed on the highway. I hated cruising at 70 mph, that's right where it's the loudest drone. so I always drove 80 on the highways, but it sucked when there were cops around.

03Grandam
03-04-2009, 06:56 PM
I ended up taking the cat off and I gutted with with a crow bar and then stuck it back on.
I haven't had any codes show up yet.

Exhaust really isn't much louder but you definitely hear more noise coming from the cat.

Sparky'sGA01
03-04-2009, 08:58 PM
I have my cat completely removed wit a straight pipe put in its place with 2 1/2 inch exhaust from where the cat was all the way back to a camaro set up 80 series flowmaster muffler with dual tips.

removing the cat made a huge difference in sound. but check engine light never comes off. the 2 1/2 inch exhaust with the cat still on made a big difference too...

Black Knight
03-05-2009, 09:39 AM
There is an 02 past the cat that might throw a code. So far you seem lucky. Ive removed the muffler and left nothing there and its loud, it sounds nice though for no muffler. Im going to remove the resonator and put on a magnaflow and see if I like the sound otherwise Im going straight piped. Its loud now without a muffler but the drone isnt bad at all.

blondiez24gt
03-05-2009, 01:15 PM
My brother has a 99 escort zx2 with a downstream o2 sensor. He removed the cat, and hasn't popped a code yet. Its been a couple weeks. I'm not sure if the grand am would or not though.

cardude007617
03-05-2009, 02:34 PM
meh put a high flo cat in (50 bucks to your door on ebay) and you'll see/hear/feel similiar results. i have one in mine (plus a pacesetter cat back) and i love the entire package.

aeh5126
03-05-2009, 02:44 PM
I was thinking about removing my cat too. I have removed my resinator and also added a Magnaflow muffler. It sounds alright but not loud enough for me. What are you guys going to do when inspection comes around? There is no way a vehicle without a cat will pass.

ryanbgb22
03-05-2009, 02:47 PM
I was thinking about removing my cat too. I have removed my resinator and also added a Magnaflow muffler. It sounds alright but not loud enough for me. What are you guys going to do when inspection comes around? There is no way a vehicle without a cat will pass.

I've never had them look under my car. You can get a fake o2 sensor / simulator or whatever, and won't get any codes.

cardude007617
03-05-2009, 02:47 PM
if the PCM is modded and they don;t VISUALLY inspect your car for one it should pass. i think?

aeh5126
03-05-2009, 02:55 PM
Yeah, whenever I go for inspectioin they don't really look at it. The just plug it into the computer and like 5 minutes later they are putting new stickers on and I'm pulling out of the garage. Would it be cheaper to get a highflow cat or an "02 simulator"? And where would I get an 02 simulator?

AaronGTR
03-05-2009, 07:21 PM
I was thinking of taking my cat off and gutting it and then putting the pipe back up so it looks stock.



My question is this, is there anyone of does anyone know of someone who took their cat off. I'm curious to know if my check engine light is going to come on and any other problems that I may incur.


I want a better sounding exhaust and a little more acceleration out of it, I dont want to take the stock exhaust off either. I dont want those ****ty sounding after market exhaust that are loud as hell.


Gutting the stock cat is a stupid idea. If you don't want a "****ty sounding after market exhaust that are loud as hell" as you put it... because having no cat will make it much louder and it makes the exhaust note sound terrible (I know because I tried it myself in the past running a straight pipe).

It doesn't give a very significant power gain on a street driven car with few mods, and it pollutes and is technically illegal. And YES it will set off a check engine light because of the post cat O2 sensor. There are ways to fix it so the check engine light doesn't come on, but they are best left for when you are replacing the cat with a high flow unit. If you want more sound and more power, getting a high flow cat and removing the resonator would do that... but it won't make a whole lot of difference. Replacing the rear exhaust is much more effective, but you said you don't want to do that... which makes me wonder if you really need/want more sound and power to begin with, and if you should even bother modding your car. I think you should just leave it alone if it's not broken.

2000GAGT
06-29-2010, 07:19 PM
i recently removed the resonator and cat. Aaron is right, removing the cat makes it much louder. First i did the resonator and it barely made a difference in sound, only noticeable if you are standing near the back of the car and driving i could barely tell. Then did the cat and it sounds pretty cool but at certain rpms gives you that "rusted muffler/old honda" sound.

After about 200 miles no codes yet but im wondering with my downstream o2 it has a lot of miles and may have lucked out and its just not reading correctly. I watched my o2 sensors on my data logger on a line graph and the downstream only gets a similar value of the upstream when i hit the gas hard. Otherwise its about the same it was when the cat was on :)

AaronGTR
06-30-2010, 03:28 PM
That is really weird. Do you have a tuned PCM? If you have no cat, you should DEFINITELY be getting a DTC code for cat efficiency from the rear O2.

westerndragon
06-30-2010, 04:32 PM
what about the rotten egg smell from removing the cat.? its hard to pick up chicks when you smell like sik. lol

as for your no SES your lucky and really your just cheaping out on your exhaust you should go to auto zone and buy fake vents and TA scoops to go on aswell, dont forget the cheap chrome edging.

if you want to eliminate the cat and res buy a cut out and place it pre-cat that way you can still pass inspection (with the cap on the cutout) and still get the straight pipe sound your looking for. IMO if all you have is a cut out w/ no CAI or headers its gonna sound like ass

SikMindz
06-30-2010, 04:57 PM
what about the rotten egg smell from removing the cat.? its hard to pick up chicks when you smell like sik. lol


Really?

REALLY?

Seriously- get a "tuner" exhaust and be done with it. It sounds like all you're after is the sound and there's nothing that's goign to be louder or more annoying.

Y2KGA
06-30-2010, 06:46 PM
According to the service manual, the cat test will occur once the car has been running between 1500 and 2500 RPMS for 5 minutes after running (at any speed) or 10 minutes. If you only drive locally or drive really fast on the highway, the test probably hasn't run yet.

If you really want to find out if the code will be set, you should set the cruise at 55mph for at least 5 minutes.

westerndragon
07-01-2010, 10:06 AM
lol sik im jus' playin'

SikMindz
07-01-2010, 11:26 AM
lol sik im jus' playin'

I know but you could at least be funny. You and PL must have gone to the same school of Laughademics and it seems that newbie with the ginger gf is a fresh recruit. lol

PhantomLover007
07-01-2010, 12:48 PM
I know but you could at least be funny. You and PL must have gone to the same school of Laughademics and it seems that newbie with the ginger gf is a fresh recruit. lol

http://www.spelledsideways.com/home/images/bush_finger.png

AaronGTR
07-01-2010, 03:37 PM
^ I don't care who ya are, that's funny right there! lol

2000GAGT
07-05-2010, 11:56 AM
i do have a tuned PCM from a long time ago but if it was removed i was never informed. I just noticed when watching both O2 sensors on a line graph the chart appears similar before and after the cat removal.

Just drove to Wisconsin and back this weekend, about another 300 miles and still no code.

2000GAGT
07-05-2010, 10:34 PM
just to follow up,

there is really no smell coming from the car except for a few seconds on cold starts if the fan is on and im running rich with the supercharger setup, which is just as loud so the exhaust is still pretty quiet. Cruising at 70 mph you can only hear the exhaust if sitting in the back seat.
We dont have emissions inspections in MN so im not worried about that. but if i ever need to change the setup it only took me 10 mins to do with a exhaust pipe cutter.

Using my data logger before and after showed a gain of 11whp for removing both cat and resonator. Very cheap mod for power but definitely a matter of opinion if its worth it or not.