No cats that bad?

[BAP56049]

Well I went to the local muffler shop today and told them I want true duals x pipe straight pipes and the guy was ok with everything and then I told him I wanted to cats cut off and he looked at me like I was from outer space. He then explains how "bad" it is to cut off the cats like the truck would explode if I did. So I was like ok well thats great I know plenty of people who have done it and had no problems. Then he starts like asking me who my parent6s are and what kind of neighborhood I live in like I was white trash because I want a loud truck.

So anyway he barely even agreed that he would do it but I have to bring my dad up there and let the mechanic explain the whole process of going catless. Soooo yeah is cutting your cats off THAT bad?

[SuperStepside]

You'll definatley lose your torque there. Just get some high flow cats.

[cancritter]

think duals would be questionable...your gona lose torque lm bettin...bin der done dat...
personaly if i were to go that route would go with single 3in to muffler then duals out
then theres your smog testin if you have it in your area...will fail without cats...anyway..food for thought...my duals cost me 1k...it then cost me 600 to get 3in put in...

[BAP56049]

Could someone link me to a preferred high flow cat?

[SuperStepside]

magnaflow

[Tweaks]

You're asking an exhaust guy to break the law and he is probably a bit uneasy about it. He's no doubt going to explain that to your father and put your father in a tough position to make the decision on whether or not to allow the cats to come off. You're engine won't be harmed, but the low rpm response and power will suffer.

[BAP56049]

Hmm well I think I'll go with the cats on. Any major sound differences?

[SuperStepside]

Cats off will sound louder.

[JWKVORTEC350]

Cats off will be louder, but if you leave them on, It will sound better and still be freakin loud. Just do true dual straights w/xpipe from the cats back and see how you like it.

[BAP56049]

Alright I'll see if I like it or not.

[BAP56049]

Alright I'll see if I like it or not.

[S/C Z71]

Cats on!

[RoLL1n D4rK]

high flow cats ftmfw!!!!

[JCribb]

Reason the exhaust shop looked at you like from outer space is it's a 2500.00 fine (if not more) to do what you asked. And technically by law he can't do it.

However if you were just dead set on having no cats do it yourself. Because If you go into a muffler shop and it's not there "they can't get in trouble" but only recommend you put cats on.

I own a 96 that didn't come with cats...thank you to prev owner... I did cut mine off my old 97 after second set of cats went bad...I wasn't spending more money on high flow cats that were gonna fail.

Now I'm not telling you to break federal law by removing cats, but the age old excuse "it was like that when i bought it" sure does work. :aniteef:

When I was stationed at Ft. Drum, NY, I had problems with an exhaust trying to get them to replace a cat on my old toyota...and it had one on it.

[GreaseDog]

He's no doubt going to explain that to your father and put your father in a tough position to make the decision on whether or not to allow the cats to come off.

oh really? if my dad tried to make the decision to leave the cats on any of my trucks, i'd tell him to go pound sand and buy his own truck to put cats on.

apparently you guys missed this part....

BAP56049
Registered User


Status: Offline
Join Date: Nov 2007
Member ID: 78737
Pics: My Gallery
Location: Georgia
Age: 29
Posts: 224

[Nick Z71]

oh really? if my dad tried to make the decision to leave the cats on any of my trucks, i'd tell him to go pound sand and buy his own truck to put cats on.

apparently you guys missed this part....
thats actually what i noticed first, why the heck does your dad have to come up there when your beyond a grown man?

[BAP56049]

Im 16, I put 29 for my age because I registered when I was 15 and I didnt want to go through the whole "Your not old enough to view this forum" thing

[S/C Z71]

I did cut mine off my old 97 after second set of cats went bad...I wasn't spending more money on high flow cats that were gonna fail.

If you had 2 sets of cats fail you have another problem before the cats. Cats don't just fail.

[S/C Z71]

i'd tell him to go pound sand and buy his own truck to put cats on.

It's "pound salt". :lol:

[Mkader17]

Both of my trucks I have owned have no cats, but truthfully I would rather run cats. My first truck I welding in straight pipe because the cat was 16 years old and it made the truck sound so so awesome. On my 02 model truck I went with the OBX system that features resonator that look like cats because the same setup with cats cost $600 extra.

You will not lose power without cats if the rest of your exhaust is the right size. at most you will lose about 5hp on the same setup when you add cats.

[Chevy1500z71]

no cats, no big deal. thats just preference, i have none, of course id tell you that cats suck. however, am i the only one here who has realized that his truck is 99, it has an 02 sensor after the cat. you NEED the cat unless you want to have the truck custom tuned. it will just throw a service engine light and you will go into limp mode unless you have it tuned, or diablo sport makes a good tuner if your truck is a nbs(99 could be nbs or obs, not sure what truck you have) that will alow you to run with out cats.

[SuperStepside]

Your truck doesn't go into limp home mode if you dont have cats on OBD II. Rear O2 sensors do not affect driveability. He doesn't NEED a cat. Plus he doesn't NEED a custom tune either. There are pigtails out there that fool the computer.

[Chevy1500z71]

Your truck doesn't go into limp home mode if you dont have cats on OBD II. Rear O2 sensors do not affect driveability. He doesn't NEED a cat. Plus he doesn't NEED a custom tune either. There are pigtails out there that fool the computer.

well sorry if iv provided bad information. i was pretty sure that a nbs truck needed the cats, thats why people leave the cats on them, thats why diablo sport offers an open loop tune. i think we both need to double check our info on this...

[AlpineTahoeSS]

Your truck doesn't go into limp home mode if you dont have cats on OBD II. Rear O2 sensors do not affect driveability. He doesn't NEED a cat. Plus he doesn't NEED a custom tune either. There are pigtails out there that fool the computer.


02 Sims is what your talking about and there the biggest waste of time. I have had 3 different sets on my tahoe and they have all gone bad, at 100 bucks a set there worthless. Just get a custom tune and get them written out like I did.

[Chevy1500z71]

02 Sims is what your talking about and there the biggest waste of time. I have had 3 different sets on my tahoe and they have all gone bad, at 100 bucks a set there worthless. Just get a custom tune and get them written out like I did.

yea, people have trouble with those things all the time, i hadnt even considered that as an option. thats why i say custom tune.

[BAP56049]

Well I got the exhaust on today. Its straights with an xpipe and true duals. No popping all rumble. I will prolly take the cats of eventually. I have a friend with the same setup but without cats and he said he said his truck drove and acted fine without the cats.

[JCribb]

If you had 2 sets of cats fail you have another problem before the cats. Cats don't just fail.

no first set was original factory stuff at 118k and when i removed the last set it had 145k. I would say altitude adjustment from okla to new york was a contributing factor. And the replacement cat pipe assy I bought was from summit...not sure how good they are but I know it wasn't the magnaflow's you guys speak of.

I never had O2 probs, except when I read the code for pass side cat (rear O2), something to do with catalyst efficency. It's been over a year now so it's hard to say.

My personal prefrence on OBS is no cats for sound factor, You NBS guys have a great sound with just a muffler change leaving cats on. Must have something to do with the flow of LS series motors:dunno:

[liftedz71]

no first set was original factory stuff at 118k and when i removed the last set it had 145k.
That mileage isnt that bad for converters. i guess it's really hit or miss on how long the stock ones will last and driving condition of the truck. I removed mine with 240,000 miles and replaced with high flow ones...they were still good. How come you couldnt buy a universal cat and have a shop weld it up for you rather than spending the money on the summit down pipe?

[JCribb]

That mileage isnt that bad for converters. i guess it's really hit or miss on how long the stock ones will last and driving condition of the truck. I removed mine with 240,000 miles and replaced with high flow ones...they were still good. How come you couldnt buy a universal cat and have a shop weld it up for you rather than spending the money on the summit down pipe?

I bought my stuff while deployed and had it sitting in garage when I got back. Had no probs till I got to new york where I guess the higher elevation (versus Okla) did the damage. And muffler shop in TN (fort campbell sits on KY/TN state line for those who don't know) wanted 400 I think to weld in new magnaflow cats...since the truck was registered in Okla and we dont have state inspections / sniffer tests I elected to remove them myself. Trans went out 3 months later and lost it to a con artist trans shop who overcharged and police wouldn't help me get my truck...long story A-hole trans guy kept my truck...it's still sitting down here if anyone wants to "remove it" lol

[bluridr94]

The only thing that the 02 sensors do after the cats is cause you to fail a damn smog inspection
they are the sensors that throw the catalyst efficiency code

i also do not think they control the fuel at all but i may be wrong

i thought that was what the ones before the cat and in the manifolds are for

does anyone know of a tuner or such that i could use to delete those codes

[GreaseDog]

I bought my stuff while deployed and had it sitting in garage when I got back. Had no probs till I got to new york where I guess the higher elevation (versus Okla) did the damage. And muffler shop in TN (fort campbell sits on KY/TN state line for those who don't know) wanted 400 I think to weld in new magnaflow cats...since the truck was registered in Okla and we dont have state inspections / sniffer tests I elected to remove them myself. Trans went out 3 months later and lost it to a con artist trans shop who overcharged and police wouldn't help me get my truck...long story A-hole trans guy kept my truck...it's still sitting down here if anyone wants to "remove it" lol
your truck should adjust to the altitude on its own.

you didnt get a lawyer to get your truck back legally? i know i sure as hell wouldnt let my truck go to some scumbag shop without some form of legal battle first.

[21cobra]

I have looked over this whole thread and it seems some like cats and some don't, why? If you have straight exhaust with no cats I would think that back presure might be a problem, but if you were running the same exhaust with dual mufflers, cherry bombs, whatever there should be no problem. Aren't cats only for emissions? I went to a mufflers shop and had dual exhuast hooked up (later after long tubes I will get rid of the cats) and the owner told me he does a off road system with no cats. He said that as long as he was told it was a off road truck he would have no problem removing the cats, but if you are "lying" that is on you.

[Pauly]

Rear O2 sensors do in fact do some small amount of fuel trimming, somewhere in the 1-2% range. Its a msall amount of trimming, but fuel trimming nonetheless. PCM tuning tirns the rear O2 sensor trimming off as well as disabling the error codes that occur when you remove cats/rear O2 sensors.

DEDIT Here is a cut and paste of info that deals with teh rear O2 sensors actually providing fuel trimming input. Rear O2 sensors do more than just tell teh PCM that the cats are there and functioning.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxx


The rear oxygen sensor, located after the catalyst, is used for fuel trim corrections on OBD-II vehicles.

By virtue of its location, the rear sensor is generally protected from high temperatures and much of the contamination that affects the front oxygen sensors.

In addition, the rear sensor sees exhaust gases that are equilibrated – they have already been converted by the catalyst so that there is very little residual oxygen.
This allows the rear sensor to respond to much smaller changes in exhaust gas oxygen content.

In turn, it then possible for the rear sensor voltage to remain near the 0.45 volt switchpoint.

This characteristic allows the rear sensor to be used for fuel control.

Under steady rpm and load conditions, the short term fuel trim bias can be adjusted so that the rear sensor voltage is maintained near the 0.45 volt switchpoint.

This ensures that the catalyst is getting a stoichiometric exhaust gas mixture, despite any shift in the front sensor switchpoint.

The rear fuel trim corrections are learned in KAM (Keep Alive Memory).
Internally, this system is known as Fore Aft Oxygen Sensor Control (FAOSC). Note that FAOSC learns and reacts very slowly because the catalyst, with its large/slow oxygen storage and release characteristic, is part of the control loop.
Also, this system cannot be used with a "y-pipe" exhaust where a single rear sensor would try to adjust dual front sensors.

Rear O2s if you will are a fine tune of the commanded fuel flow but are very much part of the model used in the PCM's math to correct AFR for closed loop

This means running no rear O2s or Simms will effect how the PCM computes what the fuel trims are.

Another issue is being the 02s hardware logic is expecting to see under 1 volt return from 02 and if O2s are removed the unused pins of 02 wiring connector are now prone to pick up EMI or RFI noise and confuse the PCM.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxx
peace
Pauly

[red1998]

Dang, my friend has a 305 5.0 and with cats off it sounds great and its still fast, i thought no cats was better cause cats are restricting your power...

[S/C Z71]

Not todays cats.

[Chevy1500z71]

Dang, my friend has a 305 5.0 and with cats off it sounds great and its still fast, i thought no cats was better cause cats are restricting your power...

those trucks arent affected by the cats, if there is no 02 sensor behind the cat your good to take em off. anything pre 96 had no 02 behind the cat, just one in front.

[BAP56049]

so i have a 99 NBS 5.3 if i cut my cats off do the rear o2 sensors go with them?

[Chevy1500z71]

so i have a 99 NBS 5.3 if i cut my cats off do the rear o2 sensors go with them?

no, you still have them, but they get a false reading. all you need to know is this- if your truck is newer than 95, you need either cats, or a custom tune or a diablo sport tuner to allow you to run without cats. plain and simple.

[chevy4x494]

my 97 only had 02 sensors before the cats, and how would taking the cats off cause you to lose power??? There nothing but a huge restriction in the exaust system, right?? I would think if you took the cat off and ran a single 3" pipe with a good muffler you'd gain power.

[liftedz71]

my 97 only had 02 sensors before the cats, and how would taking the cats off cause you to lose power??? There nothing but a huge restriction in the exaust system, right?? I would think if you took the cat off and ran a single 3" pipe with a good muffler you'd gain power.
In the 96-99 vortecs the cats flow really well and you would see no gains from removing them unless they were already clogged.

[BAP56049]

no, you still have them, but they get a false reading. all you need to know is this- if your truck is newer than 95, you need either cats, or a custom tune or a diablo sport tuner to allow you to run without cats. plain and simple.

when you mean "run" is that like run at all? or run without loss of torque etc.?

[Chevy1500z71]

when you mean "run" is that like run at all? or run without loss of torque etc.?

i mean run properly, your truck will run no mater what you mess with as far as hopw the ecm reads, i have no egr and i drive the truck as it is but theres nothing i can do about it, it just runs bad untill i can get a tune...

[BAP56049]

no, you still have them, but they get a false reading. all you need to know is this- if your truck is newer than 95, you need either cats, or a custom tune or a diablo sport tuner to allow you to run without cats. plain and simple.

I cut them off and I still have a good amount of backpressure and I have no custom tune etc. The truck runs the same way to me but the service engine soon light did come on. It didnt go into limp mode or anything you said it would I cant even tell a difference in the way it drives.

[Chevy1500z71]

I cut them off and I still have a good amount of backpressure and I have no custom tune etc. The truck runs the same way to me but the service engine soon light did come on. It didnt go into limp mode or anything you said it would I cant even tell a difference in the way it drives.

your right, you truck will not go into limp mode, your just smacking your ecm in the face and giving it false readings, but the false reading are from the 02s that only contribute like 3% to trimming up your fuel map. what your doing isnt good for your truck, but you probably wont notice it too much.