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Old 03-20-2012, 01:48 PM   #1
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Need expert advise on exhaust system

I have a 05 TJ unlimited with a 4.o and a automatic. I am looking to build a custom exhaust to remove the two upper small cats.

My plan is to remove the entire old system and save it.

Then install a new set of exhaust headers (install the 2 - O2 sensors in the headers), run new plumbing to the underside of the Jeep, install a new free flowing cat.

Once that is done I will make a custom eshaust pipe with two bungs for the other two O2 sensors, install a free flowing muffler and tail pipe.

Does anyone on this forum see any problems with what I am attempting (other than I am removing two cats)? I will have to lengthen the wires to the O2 sensors under the Jeep. Do you think / believe it will throw any codes, any unforeseen problems / issues?

Thanks for your time in advance.

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Old 03-20-2012, 01:53 PM   #2
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I don't have any advice other than to wish you good luck with it. I wish I could do that very same thing here in California. California's smog laws are so restrictive that you can't even replace a cat with an aftermarket replacement cat.

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Old 03-20-2012, 01:59 PM   #3
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They haven't gotten that strict in the county I reside in yet in Virginia.

If I lived closer to the land of crime and un-planned parenthood (Washington, DC) I would probably have to have all three cats.

That is unless the Jeep would pass the sniffer test every other year.
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Old 03-20-2012, 04:15 PM   #4
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Well there is a theory that you will lose all of your back pressure when you put in a free flowing cat which would in turn not give you low end torque.
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Old 03-20-2012, 04:53 PM   #5
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If you move any O2 sensors downstream significantly I believe they will not run hot enough causing inaccurate readings and probably throw a code.

Please someone chime in if this is inaccurate.
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Old 03-26-2012, 02:05 PM   #6
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I don't believe there should be a loss of torque with the removal of the cat's. 6 cyl motors are torque producers anyhow, removing the muffler would make a difference in torque, removing the cat's should not, lowering the compression ratio will reduce the torque as well.

I did not think about the heat issue though; by moving two of the O2 sensors further down stream it might throw codes.

I used to have a 89 short bed Ford 4x4 with a 300 6cyl, I installed a free flowing cat and the truck personality changed dramaticly. The cab was cooler, not as much heat coming from the cat and I picked up 4 mpg, I changed the size of the whole exhaust system at the same time, larger diameter to make it breath.

Anyone have any idea what the temperatures should be on either side of the two smaller cat's and what the underneath cat temperature should be?

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