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removing the cats (1990)

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Old 08-08-2010, 08:47 AM   #1
jonzcustomshop
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Default removing the cats (1990)

I was looking at a exhaust system from corvette central for my 1990 that is a bolt up -from the manifolds to the mufflers, says it has provisions for air sensors, works great with thier performance chip (which I don't have) and is for "off road use only". It deletes all 3 converters that are currently in my system.

We don't have smog checks here in mt , so I can get away with using this "off road "system.

for the most part it looks to be an easy bolt on..

however, are there going to be issues with my computer since the cats are now gone?

is the air pump hooked to the exhaust system? will I have to deal with that, and are there any other plumbing issues that might come up?
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Old 08-08-2010, 09:20 AM   #2
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You won't have any computer problems.If you are keeping the stock exh manifolds then no changes to air pump except you will have to remove / plug the air line that goes to main cat
see
http://forums.corvetteforum.com/c4-t...-plumbing.html

$$ might be better spent buying long tube headers; Proven bang for buck perf on L98's

Last edited by rodj; 08-08-2010 at 09:26 AM.
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Old 08-08-2010, 09:23 AM   #3
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Computer should just adjust for the better exhaust flow.

There is one pipe from the AIR pump to the main cat. This will need to be removed. If you're not touching the headers then you don't need to worry about those air pipes.

I have had the air pump removed and the pre-cats removed on my 87.

Last edited by Lemme; 08-08-2010 at 09:39 AM.
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Old 08-08-2010, 11:36 AM   #4
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When I removed my pre cats I also replaced my main cat. I simply bought a main cat with the air inlet and reconnected it. You can also just tie up the tube somewhere.
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Old 08-08-2010, 05:27 PM   #5
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Quote:
Originally Posted by jonzcustomshop View Post
I was looking at a exhaust system from corvette central for my 1990 that is a bolt up -from the manifolds to the mufflers, says it has provisions for air sensors, works great with thier performance chip (which I don't have) and is for "off road use only". It deletes all 3 converters that are currently in my system.

We don't have smog checks here in mt , so I can get away with using this "off road "system.

for the most part it looks to be an easy bolt on..

however, are there going to be issues with my computer since the cats are now gone?

is the air pump hooked to the exhaust system? will I have to deal with that, and are there any other plumbing issues that might come up?
I just install that kit on my 87 coupe. Was some alignment issues with the mufflers. I got the Magnaflow with LT1 tips mufflers. Was interesting trying to figure out the new hanger system they use. Easier if you have a friend helping or a couple jacks to hold up the pipes.
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Old 08-08-2010, 05:42 PM   #6
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I bought the dual exhaust system with the H pipe and the one I bought fits great. I used a set of "stock" mufflers with the correct tips. I plugged the tube ( at the valve) that goes into the main cat. mine came with the O2 nut for the sensor.

no codes and no problems.

90 coupe

Last edited by RLG; 08-08-2010 at 05:43 PM. Reason: omit info
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Old 08-08-2010, 07:33 PM   #7
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If the pump is still running I wouldn't plug the line.
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Old 08-09-2010, 08:55 AM   #8
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thanks guys!
that helps me with the decision.
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Old 08-09-2010, 09:06 AM   #9
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I disabled the pump by removing the fins
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Old 08-09-2010, 10:42 AM   #10
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Before ordering the exhaust system, you might try checking with a few local muffler shops to see what they would charge for installing a system. Most muffler shops have tube benders to custom bend a system and make it fit right and connect to your existing mufflers or any other mufflers you want to use. Shops will also use a thicker wall pipe than what you get in the kits.

A shop will also weld in an O2 bung; it's a good idea to buy a new O2 sensor as most old sensors will have rusted themselves in place after the years.

Try to find a small independent shop. It's technically a violation of federal law to remove existing working cats from a car and a shop can be fined for doing that if they get caught. It's in the 5 figure range But you can remove the old exhaust yourself, put the car on a trailer (or drive it), remove the license plates for the day and take the car to the shop. Then you tell them it's "for off-road use only".

Ask them to add an X-pipe in the spot where the main cat was located. That will reduce interior resonance and provide a better sound note. There will be no codes from removing the cats or leaving the one air pipe that went to the main cat open. But the O2 sensor has to be connected and working otherwise that will set a code.
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Old 08-09-2010, 01:53 PM   #11
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FYI, I paid $254.00 for the complete H system (minus mufflers) plus freight. All the factory hangers worked.

it had the nut for the O2 sensor already on it.
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