i was thinking of taking my cat off and just running a test pipe... woudl i loose all back presure, and then torque? and if anyone has done it what does it sound like? thansk
Took mine off when the cat melted down, I kinda liked the sound of it on the way to get another one but the wife didn't. You need enough pipe on it to keep a reasonable amount of backpressure but maybe cutting it off at the cat will be enough?
^ Bump for a thread that shows up in google but offers completely incorrect information.
NO ENGINE NEEDS BACKPRESSURE EVER. Delta pressure perhaps but never back pressure. Running less restrictive exhaust is always an upgrade.
For the record you'll see 5hp on your bone stock 4.0 Jeep motor by running a test pipe. Hit the dyno and see for yourself. In a forced induction jeep you may see between 10-20hp gained. No it didn't loose any torque down low, it only gained some power in the midrange and on top. That's all that happened, only gains.
Cutting off the exhaust at the CAT will for sure lower hp and tq numbers because the exhaust pulse will be incorrect. You must keep proper diameter and length but with as few restrictions as possible.
I hit this thread simply to clean up google search results as I googled test pipe and Jeep 4.0 and saw this incorrect information. As everyone knows the federal laws prohibit removing the CAT, you've been warned. One may argue that there's less chance of setting a fire without a CAT because a dry grass field and a super hot CAT = fire. I can't confirm nor deny this information but it's something to consider. If you daily drive your jeep, consider a hi-flow cat and keep the smog down for the rest of us if you will. If it's a dedicated toy, do as you will.
-Greg
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