choppin out catalytic converter

**gtpinsc** · 08-04-2008

i live in south carolina.we have no emissions testing.my question is if i decide to cut cat out is there anyway to make it not throw a code?

**SyntheticShield** · 08-04-2008

Two ways I know of.

1. Use an O2 Simulator
2. Get a tuner and delete the code

Well actually there is another way now that I think about it. I have seen people use those spark plug anti-foulers to mount the O2 sensor. It pulls the sensor out of the direct flow of the exhaust and supposedly that prevents a code from being set, though I have never tried it.

**gtpinsc** · 08-04-2008

thanks for quick reply...

**gtpinsc** · 08-04-2008

as of now i have 3.25 pulley,thrasher cai,2.5 catback with u bend delete flowmaster plugs 2 levels colder and 160 thermo... with a good set of headers , downpipe and cuttin cat out the mix any ball park figure of hp gain?

**SyntheticShield** · 08-04-2008

The catalytic converters are not quite as restrictive as most will lead you to believe. Yes, it does hinder flow to an extent, but its not the demon to flow that it is made out to be. So I personally do not think you will see any great gains but you should see some, I just dont know how much really.

**archemedes** · 08-04-2008

you gain some noise, and maybe 2 hp from the cat

**Iron Indian** · 08-04-2008

Originally Posted by SyntheticShield

Well actually there is another way now that I think about it. I have seen people use those spark plug anti-foulers to mount the O2 sensor. It pulls the sensor out of the direct flow of the exhaust and supposedly that prevents a code from being set, though I have never tried it.

Really??? Where did you hear this at? I never heard of this one before, I wonder if it really works. I'd like to talk to someone that has done it. My GFs brothers 04 GTP has a bad cat. I told him to cut the damn thing off and buy a sim. He's strapped for cash so this would defaintly save him a few bucks if he wants to do it. My PT won't work on his car unfortnuietly.

As for cats, I believe they are very restrictive. Before i finally rid my car of a cat completely I was running a Magnaflow 94009 High Flow 3"/3" Cat. As soon as I removed it with no other changes I dropped a pound and a half of boost. It was defaintly a restriction somewhat. Once it got off there, it never went back on. On the other GTP, I bought a bolt in 3"/2.5" Off Road DP to take care of any future cat problems for good.

As for noise, depends on your exhaust setup overall. My other GTP has a 3"/2.5" Off road DP bolted to a bone stock catback. It maybe a **** hair louder than stock, thats it. You hear the Thrasher CAI and the S/C well before any exhaust noise. Absoluetly 0 drone at any speeds too.

My car, its a bit louder but its a bit different too anyway. I'm running TOG headers, Full 3" Exh, 2.25" Y pipe, Stock Mufflers no cat or res. Its louder but it don't have much if any drone at all. Course most of that is thanks to the stock mufflers. When I had Turbo mufflers on there, boy it was loud, droney, and sounded like absolute ****. Best thing I ever did was reinstall the stock mufflers on that car. LOL

**gtpinsc** · 08-05-2008

Originally Posted by SyntheticShield

The catalytic converters are not quite as restrictive as most will lead you to believe. Yes, it does hinder flow to an extent, but its not the demon to flow that it is made out to be. So I personally do not think you will see any great gains but you should see some, I just dont know how much really.

what about a good set of headers and down pipe...hp gain = ?

**gtpinsc** · 08-05-2008

i have this vision in my head of havin headers , down pipe , cat to cat back exhaust...working like an hour glass works i hope this makes sense.to have a stock cat with a complete aftermarket exhaust just seems silly to me. as for me iron indian i have full flowmaster cat back dual tipped rolled tip, stock mani and stock downpipe.they sound really good not too loud but definately not quiet.sounds really mean on cold start.ill try and get some decent video and audio up as soon as i can

**SyntheticShield** · 08-05-2008

Iron Indian, I'll see if I can dig up the info on the spark plug fouler thing. Like I said, Ive never tried it so I have no idea if it really works.

gtpincs, a good set of headers will cost you a little down low but will help reduce KR and will gain you some overall power in the mid to upper rpm range. If you still have the U-bend in there, then the downpipe will be an excellent addition for you.

Im not saying that the cat doesnt have NO restriction, Im just saying that it is not as restrictive as most make it out to be. Obviously anything put in the exhaust flow is going to reduce that amount of flow by some number. You could always go with a quality higher flow cat.

**Iron Indian** · 08-05-2008

Yeah, let me know on the fouler thing, he'd really appreciate saving the $40. He wan't to get this done ASAP, hoping maybe this weekend I can fix him up.

If you got the cash, get headers and a DP and don't look back. It would be way better than just PEMs and a DP. Definatly worth it in the end...

**archemedes** · 08-06-2008

Originally Posted by Iron Indian

Really??? Where did you hear this at? I never heard of this one before, I wonder if it really works. I'd like to talk to someone that has done it. My GFs brothers 04 GTP has a bad cat. I told him to cut the damn thing off and buy a sim. He's strapped for cash so this would defaintly save him a few bucks if he wants to do it. My PT won't work on his car unfortnuietly.

As for cats, I believe they are very restrictive. Before i finally rid my car of a cat completely I was running a Magnaflow 94009 High Flow 3"/3" Cat. As soon as I removed it with no other changes I dropped a pound and a half of boost. It was defaintly a restriction somewhat. Once it got off there, it never went back on. On the other GTP, I bought a bolt in 3"/2.5" Off Road DP to take care of any future cat problems for good.

As for noise, depends on your exhaust setup overall. My other GTP has a 3"/2.5" Off road DP bolted to a bone stock catback. It maybe a **** hair louder than stock, thats it. You hear the Thrasher CAI and the S/C well before any exhaust noise. Absoluetly 0 drone at any speeds too.

My car, its a bit louder but its a bit different too anyway. I'm running TOG headers, Full 3" Exh, 2.25" Y pipe, Stock Mufflers no cat or res. Its louder but it don't have much if any drone at all. Course most of that is thanks to the stock mufflers. When I had Turbo mufflers on there, boy it was loud, droney, and sounded like absolute ****. Best thing I ever did was reinstall the stock mufflers on that car. LOL

aftermarket cats are all more restrictive than stock ones

**offroadfury6** · 08-08-2008

hey GTPSINC, when u get it going lemme know how it turned out, i stay in NC so we do the emissions test but i was hoping there would be someway to bypass all that without my check engine light. my dad say'd back in the day he'd take his cat off, beat it to death till all the pellets or BB's came out and re-install. of course we're talking about 77 and 78 TA's. he also said theres a company that makes a valve for this. when getting tested u'd crawl under the car and close the valve, when u want ur HP, open the valve and its suppost to bypass the cat and run straight thru exhaust

I think no cat would make u gain alot of HP personally, it does hold back alot.

like i said, lemme know how it turns out...

**gtpinsc** · 08-08-2008

Originally Posted by offroadfury6

hey GTPSINC, when u get it going lemme know how it turned out, i stay in NC so we do the emissions test but i was hoping there would be someway to bypass all that without my check engine light. my dad say'd back in the day he'd take his cat off, beat it to death till all the pellets or BB's came out and re-install. of course we're talking about 77 and 78 TA's. he also said theres a company that makes a valve for this. when getting tested u'd crawl under the car and close the valve, when u want ur HP, open the valve and its suppost to bypass the cat and run straight thru exhaust

I think no cat would make u gain alot of HP personally, it does hold back alot.

like i said, lemme know how it turns out...

will do im in between jobs right now...but as soon as i get it done ill let u know

**racerj782002** · 08-22-2008

Hey, new here, but I've recently cut out my cat, but I have no error codes what so ever. But I found this link, so it might help someone else that needs it!
OQCGP :: Ontario Quebec Club Grand Prix

**offroadfury6** · 08-22-2008

loll nice

**DnaProdigy** · 08-22-2008

Also you can hollow out the cat if your handy enough, i haven't done one in my GTP but i have done it in my 94 Lumina euro. I cut two |_| shaped holes in each section of the cat. I bent the metal down in both the sections, shoved a big screwdriver in there and chopped out the honeycomb like material. Then made sure i could get as much of the material as humanly possible out of the cat. I ran the car to get out the remaining small pieces and then bent the two |_| shaped pieces of metal up, welded them shut and threw a bit of black spray paint back on.

Wont pass emissions but it looks legal to the naked eye. Didn't have too much "bad" rasp either and gave it a much deeper tone, especially with the Flowmaster 50 series i had on there.

**gpracing** · 09-07-2008

cut out the catalityc and put 2 new mufflers and de sound it´s really loud jejeje sounds like a V8 lol from the Back and for the code i just separeted the sensor 2 inches from the pipe and erease the code with the tuner and after that never turn on.

**brodyman** · 09-07-2008

I've got an 03 gtp that I cut the cat,u bend and resonator out and installed a 3" pipe in its place. Well I actually flanged the whole thing so when I take it for the e test I can put it back in! I put an o2 simmulator in because it was turning on the check engine light. It has more throat to it like it should but not bad. I was told the stock mufflers don't flow that bad so I left them on.