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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

remove cat or precat?

 
Old 05-06-2019, 08:50 AM
  #21  
TheGreek!
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Originally Posted by leesvet View Post
sure....
punch out the pre cats and the main. I am a FIRM believer in giving the gov what they want. Never screw with the people that can make life difficult. As long as they SEE a cat they assume that it IS a CAT. Until you have to TEST...seeing a cat is good 'nuff.

Empty? maybe so..but it LOOKS legit.

The hot ticket for a budget upgrade is a set of LT exhaust manifolds. Go find a set of those to stick on your L98 and it is a big improvement. The port problem is resolved and things get better instantly. The LT ex manifolds fit too....just like the L98 stuff.
If you hollow out the cats will it cause the check engine light to come on and make the computer throw some codes? I want to do that to my '96 LT1 and LT4 cars but don't want it to make the computer throw codes and turn on the check engine light.

Last edited by TheGreek!; 05-06-2019 at 08:51 AM.
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Old 05-06-2019, 08:57 AM
  #22  
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Originally Posted by 65Z01 View Post
I had the front Y replaced with 2 1/2" mandrel-bent SS and a Random-Tech hi-flow main cat installed on my prior '88 and it always easily passed the OH sniffer test back when they still required such testing. And yes there was a nice power gain.
A 2 1/2 front y without the pre cats and either a high flow or gutted cat or straight pipe is probably the BEST mod for the money(under $300) you can do on these cars today driving around with 28-35 year old cats and xxxxxx miles A Random Tech cat is great I had one one my 90 20 years ago but hard to find today you can go cheap just get the y pipe($147 from summit) and punch out the main cat with a large screwdriver and mallet and I will put that power gain up against any of the $1000+ Catbacks like Corsa on cars with original cats sure when knew you start with a Catback but NOT today and it’s silly to put arsoecially a high dollar Catback on a car with old and malfunctioning cats but it happens all the time...

Last edited by Y-bodluvr; 05-06-2019 at 09:01 AM.
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Old 05-06-2019, 09:04 AM
  #23  
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Originally Posted by TheGreek! View Post
If you hollow out the cats will it cause the check engine light to come on and make the computer throw some codes? I want to do that to my '96 LT1 and LT4 cars but don't want it to make the computer throw codes and turn on the check engine light.
Yes as I said the 96 cars are the exception as they have OBD II systems you will need a re-tune
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Old 05-06-2019, 09:51 AM
  #24  
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Originally Posted by Y-bodluvr View Post
Yes as I said the 96 cars are the exception as they have OBD II systems you will need a re-tune
What parameter(s) in the OBD2 system needs to be changed to compensate for the lack of catalytic converters and not turn on the check engine light? What would the parameter(s) be changed to?

Last edited by TheGreek!; 05-06-2019 at 09:56 AM.
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Old 05-06-2019, 11:18 AM
  #25  
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Thanks for the "Education". I basically keep the emissions equipment working to avoid trouble. We in Virginia are getting closer to California every day with our ridiculous laws.

A State Trooper I know says the same as somebody posted above. "You may remove the equipment if inoperative but it has to be replaced with a similar part."

My VW (water cooled) actually passed the emissions testing here in Virginia without it's catalytic converter.

I was under the impression that when the EGR system is removed including the temperature sending unit the computer will give you a check engine light. Having an aftermarket exhaust system I have never had any issues with my OBD1 in my 1988 Coupe.

There are hundreds of C4's that have had their emissions equipment removed, we hear some of their problems occasionally here. Since it is YOUR Corvette you can do whatever you want to it.

I see myself as just the "temporary owner" of either of my Corvettes and I feel responsible to pass them on after my ownership and I would like to have it all working the way it was designed . I save all the parts from my cars and box them with labels so the next owner can remove my modifications and restore it to stock condition if that is what they want. I hope someday 50 years from now somebody might like driving a 1968 Corvette Roadster with a tweaked 427.

Here is some of what I found:
"You may remove an emission system or device at any time if you are replacing it with one that is specified for that vehicle and is equally effective in reducing emissions. For example, it is acceptable to replace the engine of a vehicle if:
  • the replacement engine is certified by the EPA;
  • the replacement engine is compatible with the vehicle chassis and all applicable emission control systems and devices are properly installed and operable; and
  • the resulting vehicle is identical, with regard to all emission-related parts and engine design parameters and calibrations, to the same or a newer model year vehicle, as originally equipped.
A damaged or missing catalytic converter may be replaced with an original equipment manufacturer's catalytic converter certified for that vehicle or an aftermarket catalytic converter that meets the emissions requirement for that vehicle. However, all aftermarket converters must be certified and assigned an EPA number. The EPA number should be visible.

An older engine may be installed in a newer chassis if all emission control systems and devices are connected, including the exhaust system and catalytic converter, and the resulting engine-chassis configuration conforms to the engine configuration of the model year of the chassis or newer."



Here is another very clear speaking document that describes "tampering" with a vehicles emissions system from the EPA:
https://nepis.epa.gov/Exe/tiff2png.c...5C9400062S.TIF

Take a quick look and you will probably be surprised! I know that the law is much more strict than I had previously thought.

Corvette Owners are great people and I understand the NCRS guys and I understand the modifier. You both have reasons for doing what you want to your Corvette. We should enjoy our Corvettes to the fullest but within the law (for the most part)...

I apologize if I stepped on any toes out there.
Best Regards,
Chris
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Old 05-06-2019, 12:05 PM
  #26  
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Originally Posted by TheGreek! View Post
What parameter(s) in the OBD2 system needs to be changed to compensate for the lack of catalytic converters and not turn on the check engine light? What would the parameter(s) be changed to?
You will get a code PO420 Catalyst System Efficiency Below Threshold you can either tune the rear oxygen sensors out through the PCM or install O2 “simulators” that trick the computer to not set a code
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Old 05-06-2019, 12:14 PM
  #27  
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Originally Posted by ctmccloskey View Post

I was under the impression that when the EGR system is removed including the temperature sending unit the computer will give you a check engine light. Having an aftermarket exhaust system I have never had any issues with my OBD1 in my 1988 Coupe.
I think you mis-read my post this is correct removing EGR WILL set a code on any year C4 on OBD 1 modifying/removing exhaust system WILL not or catalytic back on OBD2(96)

Last edited by Y-bodluvr; 05-06-2019 at 12:16 PM.
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Old 05-06-2019, 12:51 PM
  #28  
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Originally Posted by Y-bodluvr View Post
You will get a code PO420 Catalyst System Efficiency Below Threshold you can either tune the rear oxygen sensors out through the PCM or install O2 “simulators” that trick the computer to not set a code
Where can I get the 02 simulators at?
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Old 05-06-2019, 01:30 PM
  #29  
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Originally Posted by TheGreek! View Post
Where can I get the 02 simulators at?
http://www.bigdaddiesgarage.com/straight-cel-fix.html

Last edited by aklim; 05-06-2019 at 02:58 PM.
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Old 05-12-2019, 12:43 AM
  #30  
The Thomas J
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I noticed my Vette wasn't as loud as it used to be, It was actually downright quiet. It was like someone snuck in my garage at night and took my flow, Masters off and replaced them with a normal muffler. the power was down, I could drive it around town ok, but, flooring it did nothing. I came to the realization that one or more of my Cats were clogged. Today I brought it in for its annual inspection. Since the car is over a certain year now it's just a $10 safety inspection in NYS. After being inspected I drove it down to the muffler shop I routinely do business with. For $300 they ripped out all 3 cats and welded in straight pipes. The mechanic even cut a hole and welded a socket for the sensor to plug into and connected it. 2 of the 3 cats were completely broken up and clogged. The driver side pre-cat was hollow as the element apparently melted away from the heat. I am thrilled with the results. No check engine light, the car sounds like it's supposed to sound with a flow master exhaust. The power is back, the fuel economy went from 10 MPG to 17MPG, it starts up easier hot or cold and runs cooler. I put a 180* thermostat in last year and couldn't figure out why it wasn't running at 180* and I was getting a flashing low coolant light. I thought the sensor was bad. That's all gone away. The car is fun to drive again. It was well worth the money.
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Old 05-12-2019, 10:35 AM
  #31  
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Originally Posted by The Thomas J View Post
I noticed my Vette wasn't as loud as it used to be, It was actually downright quiet. It was like someone snuck in my garage at night and took my flow, Masters off and replaced them with a normal muffler. the power was down, I could drive it around town ok, but, flooring it did nothing. I came to the realization that one or more of my Cats were clogged. Today I brought it in for its annual inspection. Since the car is over a certain year now it's just a $10 safety inspection in NYS. After being inspected I drove it down to the muffler shop I routinely do business with. For $300 they ripped out all 3 cats and welded in straight pipes. The mechanic even cut a hole and welded a socket for the sensor to plug into and connected it. 2 of the 3 cats were completely broken up and clogged. The driver side pre-cat was hollow as the element apparently melted away from the heat. I am thrilled with the results. No check engine light, the car sounds like it's supposed to sound with a flow master exhaust. The power is back, the fuel economy went from 10 MPG to 17MPG, it starts up easier hot or cold and runs cooler. I put a 180* thermostat in last year and couldn't figure out why it wasn't running at 180* and I was getting a flashing low coolant light. I thought the sensor was bad. That's all gone away. The car is fun to drive again. It was well worth the money.
What has your exhaust got to do with the low coolant light? What do you mean it wasn't running at 180? Was it running higher? Probably be I would suspect since it has to deal with the exhaust that might not allow the entire exhaust charge to exit the vehicle.
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Old 05-12-2019, 11:20 AM
  #32  
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Originally Posted by aklim View Post
What has your exhaust got to do with the low coolant light? What do you mean it wasn't running at 180? Was it running higher? Probably be I would suspect since it has to deal with the exhaust that might not allow the entire exhaust charge to exit the vehicle.
if you have a restriction in the exhaust specifically a clogged catalytic Converter this can cause heat to back up in the engine and increase coolant temperatures
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Old 05-12-2019, 11:28 AM
  #33  
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Originally Posted by Y-bodluvr View Post
if you have a restriction in the exhaust specifically a clogged catalytic Converter this can cause heat to back up in the engine and increase coolant temperatures
Yes, that part I get. What I don't get is how does it affect the coolant level? If it is low, it should be higher because it is hotter (to a point). Buy clogged or not, if my coolant is at the right level, it should not trigger a "LOW COOLANT" light. Or am I missing something?
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Old 05-12-2019, 01:02 PM
  #34  
The Thomas J
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You and me both. For whatever reason, it stopped happening. I am so annoyed that it's raining today. I am dying to take my Vette out for a ride.
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