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no cats and no mufflers

 
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no cats and no mufflers - 8/13/2008 3:49:48 PM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline 		i got a question when you take your cats off people say it messes with your 02 sensor is that true and if it is what do you do about it and what does it do? askin for a friend i told him not to whats yalls opinion?
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RE: no cats and no mufflers - 8/13/2008 4:03:19 PM   
UltraKodiak400


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Status: offline 		Leave the cats. They are there for a reason. They usually contain the o2 sensors I believe. But with them your gas milage takes a drop, power takes a drop b/c of no back flow, and it pops to much. Save the trouble and buy a Flow Master 10seris. Just as loud as straights almost except better for your truck.

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RE: no cats and no mufflers - 8/13/2008 5:37:22 PM   
gmcz71


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Joined: 5/31/2007
From: Central Mississippi
Status: online 		you can cut your cats and tune for the rear O2 sensors to be turned off so it wont throw codes.

especially if you have an LS-motor, I dont suggest you do away with both.  too much loss of backpressure.

probably should just get an aftermarket muffler.

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RE: no cats and no mufflers - 8/13/2008 7:41:36 PM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline 		thanks for the help guys. But he'll probably get true dual straight pipes with no mufflers but will leave the cats alone

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Post #: 4
RE: no cats and no mufflers - 8/13/2008 8:27:22 PM   
Cledus Earl


Posts: 1346
Joined: 2/22/2006
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Status: online 		i just cut my exhaust off right behind the cab where it goes into the muffler. it's crazy how much more power i have now combined with the k&n intake. plus it sounds bad***, no popping or anything.

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RE: no cats and no mufflers - 8/13/2008 9:19:51 PM   
Foreman4504x4


Posts: 3285
Joined: 4/20/2003
From: Jacksonville , FL
Status: online 		I'd leave the cats on. Like UltraKodiak400 said, they put them on for a reason. Running no cats is bad for your engine. Find a good aftermarket cat converter and run true dual Flowmasters or Dynomax Bullets.

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Post #: 6
RE: no cats and no mufflers - 8/14/2008 11:17:46 AM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline 		Alright but what do yall think about true dual straight pipes with 2 1/2 pipe with 4" tips with cats and no mufflers hes goin for that extremly loud poppin and crackin noise

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Post #: 7
RE: no cats and no mufflers - 8/14/2008 11:41:43 AM   
Dock Rocker

 

Posts: 72
Joined: 2/27/2008
From: Jackson, MS
Status: offline 		There are usually 4 o2 sensors.  The front two measure the air fuel ratio so the computer can make adjustments to the mixture on the fly.  These two are the most important.  You will have to keep these.  The rear two o2 sensors or use to measure how effective the Cat is.  You do not need this but if you dont want a service engine light and loss of engine efficency you will have to use some sort of tuning software to tune the back two o2's out.  Back pressure is needed to keep your torque down low.  The lack of back pressure will move your power up to the top of the RPM band and make it feel like a dog down low.  If you have a good muffler to add some restriction you can have the best of both worlds.  You loose the restrictive cat but keep a good flowing exaust.  Unless you are drag racing you are not going to see any gains from strait pipes, you will most likely see a loss.

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Post #: 8
RE: no cats and no mufflers - 8/14/2008 1:03:48 PM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline 		thanks for that indepth speach seriously not tryin to be a smart @$$
But yea he'll definitly be leavin the cats alone and hes not really tryin to gain any performance out of it just have a really loud truck

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Post #: 9
RE: no cats and no mufflers - 8/14/2008 8:01:27 PM   
HondaGuy


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From: Onancock, VA, USA
Status: offline 		Backpressure is not a good thing, you don't want any at all. If you run properly sized pipe you can do just fine without the cats or mufflers. But for simplicity and leagality I would just leave them there and run straight pipes the rest of the way. It will be loud that way.

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RE: no cats and no mufflers - 8/14/2008 8:35:11 PM   
popnfresh24

 

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From: mcintosh minnesota
Status: offline 		ah no......... backpressure is a good thing, you have to keep backpressure so you dont burn your valves and so you can actually keep power. the only way you can go with out running any backpressure is if you are running a super hopped up engine that can run open headers....thats the only way no back pressure will work

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Post #: 11
RE: no cats and no mufflers - 8/14/2008 8:53:40 PM   
03_VINSON


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From: Pamlico County NC
Status: offline 		Older trucks don't have to have cats... I dont no the cut off line but mines a 85 and they cut mine off because they said mine were messed up anyway

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Post #: 12
RE: no cats and no mufflers - 8/14/2008 9:03:43 PM   
Guest
 A good muffler will be tuned for the certain truck or car you ordered it for.  It should keep enough back pressure to make the car or truck run at its best peaks.  I run a flowmaster with the cats gutted on my Tahoe and it made a world of difference on my performance, towing, and mileage.  The converters are for the EPA regulations. 

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RE: no cats and no mufflers - 8/15/2008 9:04:37 AM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline
quote:

Older trucks don't have to have cats... I dont no the cut off line but mines a 85 and they cut mine off because they said mine were messed up anyway
 

I think the cut off line for chevys is 96' is when they started puting O2 sensosrs in the trucks




quote:

ah no......... backpressure is a good thing, you have to keep backpressure so you dont burn your valves and so you can actually keep power. the only way you can go with out running any backpressure is if you are running a super hopped up engine that can run open headers....thats the only way no back pressure will work   



So you can burn up your engine runnin straight pipes?  But like honda guy said i heard if you run a small enough pipe like 2 1/4" you wont have to worry about back pressure

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Post #: 14
RE: no cats and no mufflers - 8/15/2008 6:06:05 PM   
HondaGuy


Posts: 1101
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From: Onancock, VA, USA
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quote:

ORIGINAL: popnfresh24

ah no......... backpressure is a good thing, you have to keep backpressure so you dont burn your valves and so you can actually keep power. the only way you can go with out running any backpressure is if you are running a super hopped up engine that can run open headers....thats the only way no back pressure will work


I am right on this one sorry, backpressure is a bad thing, however it is the easiest way to stop the valves from overheating and burning. If you run PROPERLY sized exhaust pipe then you will never have a problem. If you run 3" straight pipe true duals on a small V8 like (Dodge 4.7, Chevy 4.8, or Ford 4.6) then yes you will probably lose low end power and burn valves over time. But if you make it reasonable sized like 2-2 1/4" then you will be fine. The smaller the pipe the faster the exhaust flows through it but the pipe has less volume so even though the gasses are flowing faster less of it is going out, that acts like backpressure in a way but it doesn't restrict flow. You don't have to have a dragster motor to run open headers I did it for over a year on a bone stock 158 hp 2BBL 400 79 F-150, it ran perfect and is still like it 3yrs later, no burnt valves.

I'm not saying that type of exhaust is the best way to go,just if you use your head and pick a reasonable pipe size then you can do it very reliably and have a VERY loud truck. The truck probably would have more power if you got rid of the cats and put some good mufflers on it with an X-pipe.

< Message edited by HondaGuy -- 8/15/2008 6:07:58 PM >

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Post #: 15
RE: no cats and no mufflers - 8/15/2008 8:42:16 PM   
rednk123


Posts: 46
Joined: 7/27/2008
From: Raleigh, NC
Status: offline 		no he definitly has the 5.3 i went and looked with my dad at an 08 crew cab 4x4 chevy with the 4.8 and he had it in tow haul mode and it still didnt even come close to the 5.3 but its not really about hp with the 4.8 aint really much diff. than the 5.3 but its the torque or how ever you spell it but do yall think he'll be alright with a 2 1/2" - 3" pipe on a 5.3

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Post #: 16
RE: no cats and no mufflers - 8/15/2008 11:15:42 PM   
CTownForeMan


Posts: 3238
Joined: 7/15/2001
From: River Bottoms of Deadwood, TX
Status: offline 		If he is doing this to a new truck I say don't do it by far.  This not only will mess up everything but will freak out the computer or pcm and then you will have problems. 

Running straight exhaust no matter what size pipe will burn up the valves.  It's all in the fuel air ratio you through into the truck.  Backpressure is a good thing. 

Hope he is ready for a lot of tickets.  Government is getting strict on that kind of stuff.

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RE: no cats and no mufflers - 8/16/2008 12:38:28 PM   
HondaGuy


Posts: 1101
Joined: 3/15/2008
From: Onancock, VA, USA
Status: offline 		If you leave the cats on then 2 1/2" true dual straight pipes will be fine on it and you won't really lose any power down low. If you go any bigger then that on a stock motor then you will start losing low end.

quote:

Running straight exhaust no matter what size pipe will burn up the valves.  It's all in the fuel air ratio you through into the truck.  Backpressure is a good thing.   


You do know he is talking about a fuel injected truck not an atv right?! The computer is more then capable of correcting the air/fuel ratio after an exhaust change thats what the front O2 sensors are for, measuring the air/fuel ratio and sending that info to the computer so it can make on the fly corrections. If you look at the PCM data with a scan tool and look at the air/fuel ratio or O2 sensor output, its constantly switching from lean to rich in order to keep the ratio in the proper place. This is OBVIOUSLY something you don't have your info right on, so please do some reasearch on it before trying to call out another ASE Master certified GM Dealership Tech out on this subject. I AM right on backpressure, its a crutch used by people that don't know any better.

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RE: no cats and no mufflers - 8/16/2008 10:22:37 PM   
CTownForeMan


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From: River Bottoms of Deadwood, TX
Status: offline 		The computer is more likely to freak out if something drastically changes right away.  I do not and will not recommend straight exhaust on any truck.  Too many things to go wrong.

Pretty sure i'm not talking about an atv.  This seems to be the truck forum atleast.

ASE certified gm tech huh?  Know many of them and they would never reccomend or inform somebody on how to run straight exhaust on a new truck.  Great work.

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RE: no cats and no mufflers - 8/17/2008 12:37:15 AM   
HondaGuy


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Status: offline 		I would generally agree that drastic changes will confuse the computer, however the computer and all of its sensors on that 5.3L are more then capable to compensate for a different exhaust. I call a drastic change a cam, supercharger, head work, or stroker kits, an exhaust change is by no means a drastic thing. My 99 Dakota 318 4x4 gets a new exhaust setup every couple of months, can't really find one that I like, its never freaked out and the check engine light has not come on yet even with the cat gutted. My 02 Dakota 4.7 has had a True dual catless setup with Spintech mufflers for over 4yrs now and has never freaked out or run bad because of it, quite the opposite as it has run a best time of 14.21@93mph in the qtr with simple bolt ons and a set of 27" slicks.

I know many other ASE certified Techs that would also say that doing this to a new truck is a bad idea, I feel as a younger tech that it is my responsibility to help the "young and dumb" crowd do things to their vehicles that many expecially older people don't agree with, but in a safe manner. Frankly no matter what you might think the best thing is, people like him and I are going to do things like this to our trucks and cars no matter what, so at least I can help by telling him the safest way to do it. It is the same arguemant that I am having at work right now with the older and more stubborn techs at my dealership, they are afraid that if we get into the GM Performance Parts and TRD Parts that we will get burnt by the warrantys. My argument is that the people that are willing to do this to their vehicles are going to do it no matter whos selling the stuff, it might as well be us. As I said above I don't think this is the best setup, BUT all he is interested in is the sound, he cares little about power, straight pipes are what he is looking for if he wants just noise. So I will say again, he IS fine running straight pipes on his truck if he runs the right size and cares nothing about any warrantys that might be left.

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Supertrapp Mudslinger
HL EPI Clutch Kit
Relocated Radiator
Permacool 8" electric fan (covers the whole radiator)
12x7 ITP C Series Type 5 wheels
27in Bi/Tri Claw Magnum combo
Viper Max 3000lb winch Red Amsteel rope
Mud guard fender flares A-arm skid plates

88 Yamaha Banshee red and grey
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Post #: 20
RE: no cats and no mufflers - 8/17/2008 10:22:24 PM   
PRAIRIEMAN


Posts: 558
Joined: 10/15/2003
From: N.M.B. South Carolina
Status: offline 		I cut mine off and put a flowmaster on it and my engine light went off and I picked up power and gas milage. I have a 01 5.3

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RE: no cats and no mufflers - 8/18/2008 11:32:33 AM   
CTownForeMan


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From: River Bottoms of Deadwood, TX
Status: offline 		Thats not my point.  Warreny is not orth a crap now a days.  We are having nothing but trouble at work for emmisions and I deal with diesel's.  Gasolines are by far worse and tellin people to run straights lead to nothing but bad emmisions and tickets.  These type of things here are why we are having to install DPF system on diesel's and restricting power and milage.  Trying to get the air cleaner cause nobody cares anymore.

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RE: no cats and no mufflers - 8/18/2008 9:11:58 PM   
PRAIRIEMAN


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Status: offline 		Yea, s.c. doesnt have inspections so we get away with it.

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Post #: 23
RE: no cats and no mufflers - 8/18/2008 9:49:01 PM   
BTTW

 

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Status: offline 		when you gut the cats (i do this so it still looks legal lol), as i have on old 5.7TBIs and 4.3vortecs, as said above it messes with o2 sensors, which cause it to think its running lean and it dumps more fuel which not only smells but mpg goes down. you can get it tuned out/off (the o2 sensors) as said above. Also, the 5.3 i would run a 2" or 2.5" pipe from the cat back(after gutted).  right now i have a NNBS gmc 6.0 with no cat and 44 flowmaster and its LOUD, not poppy either like most people say.

i say go for it :D thats just me though :P

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RE: no cats and no mufflers - 8/20/2008 5:47:16 PM   
HondaGuy


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quote:

ORIGINAL: BTTW

when you gut the cats (i do this so it still looks legal lol), as i have on old 5.7TBIs and 4.3vortecs, as said above it messes with o2 sensors, which cause it to think its running lean and it dumps more fuel which not only smells but mpg goes down. you can get it tuned out/off (the o2 sensors) as said above. Also, the 5.3 i would run a 2" or 2.5" pipe from the cat back(after gutted).  right now i have a NNBS gmc 6.0 with no cat and 44 flowmaster and its LOUD, not poppy either like most people say.

i say go for it :D thats just me though :P


No it does not, the rear O2 sensor has nothing to do with the air/fuel ratio they are a Catalyst (catalytic converter) monitor only. The front O2 sensor is what controls the air/fuel ratio and that is not affected by something you do behind it. I don't have a rear O2 sensor on my truck at all and it runs no different and gets no worse MPG with it gone.

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2008 Honda Rancher ES 4x4 black
Supertrapp Mudslinger
HL EPI Clutch Kit
Relocated Radiator
Permacool 8" electric fan (covers the whole radiator)
12x7 ITP C Series Type 5 wheels
27in Bi/Tri Claw Magnum combo
Viper Max 3000lb winch Red Amsteel rope
Mud guard fender flares A-arm skid plates

88 Yamaha Banshee red and grey
stockish
21" Mud Sharks

http://www.myspace.com/kotakid287

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Post #: 25
RE: no cats and no mufflers - 8/20/2008 9:54:06 PM   
nonnieselman


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Status: offline
quote:

ORIGINAL: HondaGuy

quote:

ORIGINAL: BTTW

when you gut the cats (i do this so it still looks legal lol), as i have on old 5.7TBIs and 4.3vortecs, as said above it messes with o2 sensors, which cause it to think its running lean and it dumps more fuel which not only smells but mpg goes down. you can get it tuned out/off (the o2 sensors) as said above. Also, the 5.3 i would run a 2" or 2.5" pipe from the cat back(after gutted).  right now i have a NNBS gmc 6.0 with no cat and 44 flowmaster and its LOUD, not poppy either like most people say.

i say go for it :D thats just me though :P


No it does not, the rear O2 sensor has nothing to do with the air/fuel ratio they are a Catalyst (catalytic converter) monitor only. The front O2 sensor is what controls the air/fuel ratio and that is not affected by something you do behind it. I don't have a rear O2 sensor on my truck at all and it runs no different and gets no worse MPG with it gone.




Gah.. im glad your tryin to teach them something.. Some people are just to dumb to listen..

Only thing thats goin to happen to the PCM if you gut/delete the cats is, your goin to throw codes. Thats it.

Here are the possible codes:

P0137       O2S Circuit Low Voltage Bank 1 Sensor 2
P0138       O2S Circuit High Voltage Bank 1 Sensor 2
P0140       O2S Circuit Insufficient Activity Bank 1 Sensor 2
P0141       O2S Heater Performance Bank 1 Sensor 2
P0157      O2S Circuit Low Voltage Bank 2 Sensor 2
P0158      O2S Circuit High Voltage Bank 2 Sensor 2
P0160      O2S Circuit Insufficient Activity Bank 2 Sensor 2
P0161      O2S Heater Performance Bank 2 Sensor 2

I didnt notice any loss of gas mileage when i gutted mine, but i had the full exhaust all the way to the stock tail pipe with just a small magnaflow muffler.
Didnt notice a gain or loss of power either. It made it alot louder tho. Now with the turbo i put another muffler behind it to quiet it down almost to stock levels.


If i were to do it again on a Stock NA truck. I would just gut the cats, and put a decent muffler where the stocker is.
Stock exhaust size is 2 7/8", Its actually Metric but thats what it measures. That will support plenty of flow for even a slightly modded engine.




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Post #: 26
RE: no cats and no mufflers - 8/22/2008 8:51:38 PM   
jhendersonsanity

 

Posts: 261
Joined: 12/5/2007
From: Mobile and Tuscaloosa, AL
Status: offline 		i have an 03 GMC 2500 and I have true duals from engine to tips. I cut my mufflers off but left the cats. I is loud but sounds great!!! A friend of mine has an older bronco that has true duals with no cats and no muffler, he's had no problems and is just a little louder than mine, but mine sounds much better. If I were u i would run true duals and cut the mufflers off but leave the cats.

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Post #: 27
RE: no cats and no mufflers - 8/24/2008 10:08:22 PM   
HondaGuy


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quote:

ORIGINAL: nonnieselman

quote:

ORIGINAL: HondaGuy

quote:

ORIGINAL: BTTW

when you gut the cats (i do this so it still looks legal lol), as i have on old 5.7TBIs and 4.3vortecs, as said above it messes with o2 sensors, which cause it to think its running lean and it dumps more fuel which not only smells but mpg goes down. you can get it tuned out/off (the o2 sensors) as said above. Also, the 5.3 i would run a 2" or 2.5" pipe from the cat back(after gutted).  right now i have a NNBS gmc 6.0 with no cat and 44 flowmaster and its LOUD, not poppy either like most people say.

i say go for it :D thats just me though :P


No it does not, the rear O2 sensor has nothing to do with the air/fuel ratio they are a Catalyst (catalytic converter) monitor only. The front O2 sensor is what controls the air/fuel ratio and that is not affected by something you do behind it. I don't have a rear O2 sensor on my truck at all and it runs no different and gets no worse MPG with it gone.




Gah.. im glad your tryin to teach them something.. Some people are just to dumb to listen..

Only thing thats goin to happen to the PCM if you gut/delete the cats is, your goin to throw codes. Thats it.

Here are the possible codes:

P0137       O2S Circuit Low Voltage Bank 1 Sensor 2
P0138       O2S Circuit High Voltage Bank 1 Sensor 2
P0140       O2S Circuit Insufficient Activity Bank 1 Sensor 2
P0141       O2S Heater Performance Bank 1 Sensor 2
P0157      O2S Circuit Low Voltage Bank 2 Sensor 2
P0158      O2S Circuit High Voltage Bank 2 Sensor 2
P0160      O2S Circuit Insufficient Activity Bank 2 Sensor 2
P0161      O2S Heater Performance Bank 2 Sensor 2

I didnt notice any loss of gas mileage when i gutted mine, but i had the full exhaust all the way to the stock tail pipe with just a small magnaflow muffler.
Didnt notice a gain or loss of power either. It made it alot louder tho. Now with the turbo i put another muffler behind it to quiet it down almost to stock levels.


If i were to do it again on a Stock NA truck. I would just gut the cats, and put a decent muffler where the stocker is.
Stock exhaust size is 2 7/8", Its actually Metric but thats what it measures. That will support plenty of flow for even a slightly modded engine.





Thanks for the help, I am trying some people just don't get it, even though they think they do. Have you run your truck at the track? How much faster is it with that STS setup, and how much boost does it make? I'm getting ready to start a custom turbo setup on my 02 Dakota 4.7L rcsb, going to be in the neighborhood of 400-450hp at 12psi (properly tuned of course).

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(in reply to nonnieselman)
Post #: 28
RE: no cats and no mufflers - 8/30/2008 11:49:34 PM   
backinblack700


Posts: 2988
Joined: 9/2/2006
From: GEORGIA
Status: offline 		 i have 3'' straights from the headers out the back on my '94 5.8L F-150, no cats or mufflers with 6'' tips, its crazy loud...

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