Bypassing the Cat on a 98 TJ 4.0L ? ?

[Underdog]

Hypothetically speaking if you were to remove the cat and bypass it what would the gain/loss be? (gas mileage, hp . . .)
I know backpressure can be important but how much is it a factor on the 98 TJ 4.0L engine?

Other than a banks header the exhaust system is stock. I am not looking for any real power gain. I have the Banks headers only because my exhaust manifold cracked (like most of them do).

What I am going for is and increase in gas mileage. I thought that removing the cat combined with an ARB snorkel might and eventually a Flex-a-lite electric fan may help MPG.

 

[wr250]

the cat will have no influence on fuel economy, unless its plugged. it will be detrimental to fuel economy if you have a o2 sensor after the cat. a more open exhaust (to a point) system will help with economy. probably could goto a 2.5" header to cat pipe, 2.25" cat,2.25 to muffler, 2.25 in ,2.5 out muffler,2.5 tailpipe; 2.5 to the muffler may reduce low-end a bit. i went to a 2" exhaust from header (on my toyota) to tailpipe and it made a 1 gear power difference (up hills that before required downshifting, now dont), and 3 mpg in fuel economy.

 

[Badger]

not going to happen.first jeep uses a pretty free flowing cat as it is.second your jeep uses two O2 sensors ,one before and one after.if it doesn't see a change in the exiting gases it will go register an engine code.

 

[mbryson]

Modern monolithic cats are not very restrictive at all (if any). I'd leave it and save the environment. (I think the engine could run poorly without it. Our '96 ZJ with OBDII {what I believe the '98 TJ has} has two O2 sensors. One is in the cat and one in the regular place.)

 

[crimsonride]

You're sure to get jumped all over for it. Especially come time for inspection. Don't bother with so called "high-Flow" cats either. Any cat that's not low quality is pretty free flow since no manufacturer will pack more of the expensive metal inside the cat than necessary.