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Cut the Cat?

B

Bored400

NAXJA Forum User
Location
Grand Junction, CO
Has anyone ever just deleted thier catalytic converter? Straight piped it? Out here in the "Old West" we dont have to worry about emissions...yet...but anyhoo, I was just wondering.
 
I'm not trying to get anyone to incriminate themselves, I'm just wondering if it would have an adverse effect on performance. I've straight piped my 77 Dodge truck, and never looked back. My 89 xj has boucoup miles on the exhaust side, but it's got a brand new engine. I know that you have to have a certain amount of back pressure, but on my truck I just compensated with a little extra piping. No room for extra piping on the xj, so would a guy maybe throw a cherry bomb on there or something?
 
Its illegal by Federal Law to remove the cat from your car....but...you probably wont get caught unless you have emissions/vehicle inspection in your state...

there is an ongoing debate about whether or not removing your cat is good or bad for your engine...some say that a free flow exhaust is best...others debate that you need the cat to create proper back pressure....

if you remove it, you can probably count on 2 things - louder exhaust (depending on your muffler type)...and your exhaust fumes will be worse....smell pretty terrible...
 
I don't have one on my 88 MJ or my 90 XJ. On Renix years and OBD-I years, I feel deleting them only helped performance, but that's not to say it's legal or correct to not use one. I'm sure I'm going to end up in greenie hell for not having them, but I'll just have to deal with that when the time comes. My 99 XJ however does have one, and always will, I just don't think OBD-II responds well without them, even with a test pipe.
 
RenixPower said:
I don't have one on my 88 MJ or my 90 XJ. On Renix years and OBD-I years, I feel deleting them only helped performance, but that's not to say it's legal or correct to not use one. I'm sure I'm going to end up in greenie hell for not having them, but I'll just have to deal with that when the time comes. My 99 XJ however does have one, and always will, I just don't think OBD-II responds well without them, even with a test pipe.
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Coming from a guy with as many Jeeps as you have, I'll take it as gospel. Ahoy, Sawzall!
 
Make sure you aren't cutting out an O2 sensor. On my 98, the second sensor actually plugs into the cat, so cutting it out would probably cause worse engine performance and fuel mileage.

Midas Muffler brand will install and warranty a cat for pretty cheap ($100 or so). Why don't you just replace it??? No mess, no worries, better for the environment, and you don't have to drive around in fear that an LEO is gonna stick his nose under your rig.
 
WildernessJeep said:
Make sure you aren't cutting out an O2 sensor. On my 98, the second sensor actually plugs into the cat, so cutting it out would probably cause worse engine performance and fuel mileage.

Midas Muffler brand will install and warranty a cat for pretty cheap ($100 or so). Why don't you just replace it??? No mess, no worries, better for the environment, and you don't have to drive around in fear that an LEO is gonna stick his nose under your rig.
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You can get rid of the downstream sensor(after cat) and it will not effect performance or drivability at all. It probably won't even throw a code. All it does is monitor that the cat is working properly. I drove my 99 with it disconnected for about a week and it didn't throw a code or change the performance.
 
I thought about doing another cat. Not for the sake of the environment, and definetely not for the environMENTALists, but just so that it would remain stock. I dont think that a cat really makes that much of a difference in the grand scheme of things, but if the engine was built to have one then I thought that it should keep it. Truth be told, a well tuned gas engine puts out no more CO2 than a good long fart.
 
Don't know about the OBD2 trucks, but I have heard a high mile Renix truck with a cheapy muffler that really sounds nice with a gutted cat. One advantage of a gutted cat over just a straight pipe is that on XJ's you can see if one of our trucks has one or not, and depending on how that enforcement is done, a cop in a CV, Impala or Charger could easily tell since those cars sit fairly low.
 
Bored400 said:
I thought about doing another cat. Not for the sake of the environment, and definetely not for the environMENTALists, but just so that it would remain stock. I dont think that a cat really makes that much of a difference in the grand scheme of things, but if the engine was built to have one then I thought that it should keep it. Truth be told, a well tuned gas engine puts out no more CO2 than a good long fart.
Click to expand...
A cat is there for carbon monoxide as well as other things. Why risk the people's health near you in a traffic jam or at a stoplight. A high flow unit is $70 on ebay. If you cant afford the $70 to keep the air clean and legal then idk what to tell you. Just make sure you keep your windows up...
 
BBeach said:
A cat is there for carbon monoxide as well as other things. Why risk the people's health near you in a traffic jam or at a stoplight. A high flow unit is $70 on ebay. If you cant afford the $70 to keep the air clean and legal then idk what to tell you. Just make sure you keep your windows up...
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I agree with the idea that you should get one for $70, I've never seen that on eBay, but I believe it. However, I think you're exaggerating by saying keep your windows up and you're risking peoples' health for the 20 seconds you're at a stoplight. Keep in mind cars didn't have cats for what 75? 80? years, I doubt that many people got sick off of sitting and breathing it for a matter of seconds. I can't smell it on either of my Jeeps at stoplights, I still wouldn't stick your head right by the tailpipe, but it's really not that bad, with mine anyway.
 
I saw it for $70, idk about shipping. But in any case i saw them for $100 at a local shop that isn't exactly the cheapest. Most cars should be fine at a stoplight with out without a cat unless there's some problem with the TPS or its running rich/lean which it shouldn't because its idling and should have stoich? Im not positive but that would be my guess. In any case, do something good for the environment as well as putting some money into something made in USA :us: , perhaps if you dont care about the environment perhaps at least our economy? :patriot:
 
 
I've run vehicles cat-less doe a number of years, with no bad effects. Was thinking about doing it to the current XJ (89), but I was waiting for the new air filter/bored TB to get put in, so I could get more improvement from the freed exhaust.

IMHO, you'll not notice anything bad from not having a cat. It might be a bit louder, but you'll not smell the difference. I never truly saw any performance increase on my butt-dyno, but it may have just been out of calibration.....
 
RaccoonJoe said:
I've run vehicles cat-less doe a number of years, with no bad effects. Was thinking about doing it to the current XJ (89), but I was waiting for the new air filter/bored TB to get put in, so I could get more improvement from the freed exhaust.

IMHO, you'll not notice anything bad from not having a cat. It might be a bit louder, but you'll not smell the difference. I never truly saw any performance increase on my butt-dyno, but it may have just been out of calibration.....
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It'd be louder which could be good, but its still illegal and harmful. And of course you can't smell the difference....carbon monoxide is odorless as well as colorless and tasteless.
 
Summit has some universal high-flow cats listed as low as $53.00. Cat-Co. brand I believe. Just ordered a couple for a 1978 Trans Am we're doing for a customer...
 
Carbon monoxide is emitted anytime a fire is present. Catalytic converters are a great idea, until they go bad...then you actually end up burning more fuel for the same power. I contend that a well tuned engine, without a cat is the best of both worlds in that you use less fuel to power your rig without restriction, and you essentially put out the same amount of carbon monoxide. Any takers on that argument?
 
Bored400 said:
Has anyone ever just deleted thier catalytic converter? Straight piped it? Out here in the "Old West" we dont have to worry about emissions...yet...but anyhoo, I was just wondering.
Click to expand...
I'm picking up late on this thread... but I did this on my '93 XJ. Bought it new as US-spec (with a cat) but I was taking it to a Mideast country which had no unleaded fuel. So to avoid poisoning the cat with lead, I removed it and put it in store, and fitted the OEM pipe which adapts the XJ for leaded fuel (can't recall the part number).

Didn't affect the performance or the noise. I did wonder about the effect on the O2 sensor. As its a 93, there is only one sensor above the cat/pipe, and either it still works, or it's clogged up and the PCM runs on the default setting....

I now run the Jeep back in UK on unleaded fuel. It is now considered as a non-cat vehicle and passes the emissions test. I keep thinking of refitting the cat and maybe a new O2 sensor, but on the other hand, why bother?

br1anstorm
 
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