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Can I go catless on my 1992 C4?

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Old 01-09-2018, 10:55 PM
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Sworn
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Default Can I go catless on my 1992 C4?

Hey guy's, kind of a noob question..

My 1992 C4 is emission exempt. Bearing that in mind, can I just eliminate the cats? If I'm correct, my 1992 is OBD1. If I remove the cats will it throw a code? I was thinking of getting rid of said cats and doing a catback exhaust. I figure since the car is 26 years old the catalytic converters are probably shot anyway. My 1992 has 66K on it BTW.

Thanks in advance!
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Old 01-10-2018, 02:45 AM
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Yes, mine are gutted though instead of completely removed.
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Old 01-10-2018, 06:21 AM
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Originally Posted by Mishawaka View Post
Yes, mine are gutted though instead of completely removed.
What effect did it have? Noise, gas miiage performance, ETC
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Old 01-10-2018, 10:22 AM
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In most states, even if exempt, it is a $10k fine if you get caught with no cats. I never thought twice about it until I passed a Random spot check on the other side of the road with a mirror under the cars. I drove straight to my exhaust guy and had a hollowed out cat put on.
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Old 01-10-2018, 11:07 AM
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Originally Posted by Mishawaka View Post
Yes, mine are gutted though instead of completely removed.

No CEL? Thanks
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Old 01-10-2018, 11:10 AM
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Originally Posted by Mishawaka View Post
Yes, mine are gutted though instead of completely removed.
Originally Posted by biggiefl View Post
In most states, even if exempt, it is a $10k fine if you get caught with no cats. I never thought twice about it until I passed a Random spot check on the other side of the road with a mirror under the cars. I drove straight to my exhaust guy and had a hollowed out cat put on.

I live in The Peoples Republic of Chicago. LOL! The city is so broke they don't have money for much of anything. I'm no too worried about it. Thanks for the heads up though!
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Old 01-10-2018, 11:10 AM
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What years can you do this on? I assume there would be some benefit on the exhaust flow? I have a '95. In BFE west Texas, you will not get checked for catalytic converters.
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Old 01-10-2018, 11:35 AM
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If you have a resonator, they would probably overlook the missing cats.
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Old 01-10-2018, 12:16 PM
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The cats on the '92 can be cut off and replaced with pieces of straight pipe. Not an easy job given the location of the two cats. But the OEM cats do work to reduce emissions and they flow very well.

You may want to have the O2 sensors deleted from the ECM, A tune can do that. The '92 is an OBD1 system

As long as your state emissions laws don't require a visual inspection, you should have have any problems. Here in WA, there are no visual checks anymore, not even a sniffer test. It the few areas where emissions checking is required, they just hook the computer up to the ALDL port on the car and check certain emission values.

As to any fine, it IS against federal law to remove working cats. But the fine is typically levied against a shop when they get caught removing them. Do it in your garage or back yard and you will be pretty safe.
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Old 01-10-2018, 12:29 PM
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I cut out the cats on my 94' and replaced with straight pipe. Hated the sound and smell with minimal performance gains. It did sound good at WOT but partial throttle sounded like an old bubba farm truck. I ended up sourcing some good used cats and replaced everything. I say leave well enough alone and either do the muffler deletes or find a nice cat back that suits the tone you are after.
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Old 01-10-2018, 03:42 PM
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No CEL here with the cats gutted and resonator deleted. 92 six speed.

I guess I should add that you WILL have a smell of gas but thats a given with having no cats.

Last edited by Mishawaka; 01-10-2018 at 03:44 PM.
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Old 01-10-2018, 03:51 PM
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Can you run your Corvette Cat-less? Of course you can. The big question is why? There are plenty of postings where people have tried doing what you are going to do and found no real benefit in doing so.

I have a 1988 Coupe that no longer requires emissions testing here in Virginia due to its age. I still get my emissions tested just for my own purposes, I don't mind the cost of the test I just want to know what is happening within my engines emissions system.

About 15 years ago I installed cat back system and a new performance oriented Catalytic Converter while I was at it. The car runs clean and meets the requirements for its emissions.

Is it not in all of ours "Best Interests" to keep the emissions within the normal range? If the car was a "Track car" then I might think differently but for use on the roads I want my engine to run as cleanly as possible.

On my 1988 I found that my EGR had failed looking at the results from the emissions testing station. The car had no codes or anything to tell me it was not working properly. The emissions test results made it clear that there was a problem and the EGR was replaced and all is now well again. I could have deleted the EGR but chose to not do so to keep the emissions system functional and the car running clean.

We have a responsibility to maintain our cars properly and keep them safe so we are not the cause of problems or safety issues.

Enjoy those Corvettes out there but keep them safe for you and others to enjoy down the road.
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Old 01-10-2018, 05:57 PM
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Originally Posted by ctmccloskey View Post
Can you run your Corvette Cat-less? Of course you can. The big question is why? There are plenty of postings where people have tried doing what you are going to do and found no real benefit in doing so.

I have a 1988 Coupe that no longer requires emissions testing here in Virginia due to its age. I still get my emissions tested just for my own purposes, I don't mind the cost of the test I just want to know what is happening within my engines emissions system.

About 15 years ago I installed cat back system and a new performance oriented Catalytic Converter while I was at it. The car runs clean and meets the requirements for its emissions.

Is it not in all of ours "Best Interests" to keep the emissions within the normal range? If the car was a "Track car" then I might think differently but for use on the roads I want my engine to run as cleanly as possible.

On my 1988 I found that my EGR had failed looking at the results from the emissions testing station. The car had no codes or anything to tell me it was not working properly. The emissions test results made it clear that there was a problem and the EGR was replaced and all is now well again. I could have deleted the EGR but chose to not do so to keep the emissions system functional and the car running clean.

We have a responsibility to maintain our cars properly and keep them safe so we are not the cause of problems or safety issues.

Enjoy those Corvettes out there but keep them safe for you and others to enjoy down the road.
In regards to why.....

My thought process in POSSIBLY deleting the cats was with the consideration that they may be shot. Admittedly, I don't know the longevity or life span of a catalytic converter Considering my C4 is 26 years old I was kind of working under the assumption that they probably weren't as efficient as when new. To reiterate, I wasn't sure so I asked a question on a vehicle specific forum to learn more.

In regards to maintaining vehicles properly, I have always done my best. It is not my intention to take a two owner Corvette with no accidents and just 66K and turn it into something unsafe.
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Old 01-11-2018, 04:30 PM
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Yes you can....current 94 and past 87 have, no driveability concerns.
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Old 01-11-2018, 09:54 PM
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Drop the exhaust and hollow them out, they rob horsepower and are just one more component to fail (clog, rattle ect.) If you hollow them out then they still have the appeaance of being there, there not monitored how would you know if there still internally intact? Highly doubt you'll run into any legality issues if your car is exempt from emissions anyways.
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Old 01-12-2018, 06:11 AM
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Originally Posted by biggiefl View Post
In most states, even if exempt, it is a $10k fine if you get caught with no cats. I never thought twice about it until I passed a Random spot check on the other side of the road with a mirror under the cars. I drove straight to my exhaust guy and had a hollowed out cat put on.
Your location says Ellenton Florida. Florida doesn't require any emission testing at all, even on newer models that may require it in other emissions crazy states like say NY or CA..... so why would anyone be visually checking for cats?
Who was checking and where exactly did this happen?? I'm calling BS on your entire story!!

Last edited by mako41; 01-14-2018 at 07:29 PM.
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Old 01-12-2018, 05:57 PM
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Originally Posted by c4cruiser View Post
The cats on the '92 can be cut off and replaced with pieces of straight pipe. Not an easy job given the location of the two cats. But the OEM cats do work to reduce emissions and they flow very well.

You may want to have the O2 sensors deleted from the ECM, A tune can do that. The '92 is an OBD1 system

As long as your state emissions laws don't require a visual inspection, you should have have any problems. Here in WA, there are no visual checks anymore, not even a sniffer test. It the few areas where emissions checking is required, they just hook the computer up to the ALDL port on the car and check certain emission values.

As to any fine, it IS against federal law to remove working cats. But the fine is typically levied against a shop when they get caught removing them. Do it in your garage or back yard and you will be pretty safe.
If you delete the upstream O2 sensors, how will it work in closed loop? IF you delete the downstream ones, I would just get an O2 sim
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Old 01-12-2018, 06:01 PM
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Originally Posted by Sworn View Post
In regards to why.....

My thought process in POSSIBLY deleting the cats was with the consideration that they may be shot. Admittedly, I don't know the longevity or life span of a catalytic converter Considering my C4 is 26 years old I was kind of working under the assumption that they probably weren't as efficient as when new. To reiterate, I wasn't sure so I asked a question on a vehicle specific forum to learn more.

In regards to maintaining vehicles properly, I have always done my best. It is not my intention to take a two owner Corvette with no accidents and just 66K and turn it into something unsafe.
In my 91, the "Pre-Cats" were deleted simply because the LT headers didn't come with them and AIR or EGR so all those were deleted too. I could have kept the AIR but it made things harder to get to. The HSR intake did not have EGR so there was that.

I tried a hollowed out main cat but it was so noisy that I went to a free flowing cat or at least freer flowing to keep some noise down. I don't know anything else about the cat making it unsafe.
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Old 01-12-2018, 09:45 PM
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Originally Posted by aklim View Post
In my 91, the "Pre-Cats" were deleted simply because the LT headers didn't come with them and AIR or EGR so all those were deleted too. I could have kept the AIR but it made things harder to get to. The HSR intake did not have EGR so there was that.

I tried a hollowed out main cat but it was so noisy that I went to a free flowing cat or at least freer flowing to keep some noise down. I don't know anything else about the cat making it unsafe.
I agree. Unless I misinterpreted what was said....

Maybe the other member could clarify.
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Old 01-13-2018, 11:43 AM
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Originally Posted by c4cruiser View Post
You may want to have the O2 sensors deleted from the ECM, A tune can do that. The '92 is an OBD1 system.
Originally Posted by aklim
If you delete the upstream O2 sensors, how will it work in closed loop? IF you delete the downstream ones, I would just get an O2 sim
Yeah, I was reading c4cruiser's post and though the same as you, "Whoa!" So just to be clear, 1996 is the only OBD2 C4 they made. All prior years were OBD1. In probably all EFI-equipped cars of all years, there are O2 sensors before the cats, which the PCM uses to properly maintain the air:fuel ratio at all times in closed-loop operation (closed-loop is any time the car is warmed up and not running at or near WOT). You do not want to remove or delete these sensors in real life or in the software tune. If you did, you'd have a car running in open-loop all the time.

OBD2 cars (1996+) also have a second set of O2 sensors after the cats. These only exist to allow the PCM to test the function of the cats: it compares what's coming out of the cats with what's going in and uses that info to assess whether the cart is working well or not. The PCM does not use these post-cat or "downstream" sensors to manage the fuel mixture. If you remove or hollow out the cats on an OBD2 car, it will quickly through a trouble code because the PCM knows the cat isn't functioning anymore. If you remove or disconnect the downstream O2 sensors it will do the same thing. In order to avoid the CEL, you have to either modify the PCM tune to turn off that diagnostic test, or somehow trick the rear sensors into giving the PCM the signal it's looking for. Doing it in the tune is the proper way to achieve this. This is the step that c4cruiser was referring to in his post.

They key is this: any 1984-1995 C4 is OBD1, and (to my knowledge) won't even have the downstream O2 sensors. They have no way of testing their cat function, so they can't tell if it's missing or hollowed out (or on there and working well). So there is nothing to disable or worry about. You can remove the cats or whatever, and the ECM won't know the difference.

As to whether that's a good thing to do or not, I'll let others address that question!
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