Anybody put a straight pipe on their 4.0?

It will sound like shit, believe me.

I removed the third cat on mine, and even just removing that made it tremendously louder.

As for gas mileage, you certainly won't gain anything if that's what you're wondering. I'd venture to say of anything you might actually lose MPG.

But is anyone really keeping track on a Wrangler?
 
It will sound like shit, believe me.

I removed the third cat on mine, and even just removing that made it tremendously louder.

As for gas mileage, you certainly won't gain anything if that's what you're wondering. I'd venture to say of anything you might actually lose MPG.

But is anyone really keeping track on a Wrangler?
Yours would not have been nearly as loud if your exhaust shop knew anything about how to do exhaust. Hard mount that shit to the frame and I promise you it won't be quiet.
 
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Yours would not have been nearly as loud if you exhaust shop knew anything about how to do exhaust. Hard mount that shit to the frame and I promise you it won't be quiet.

Actually, before they even mounted that exhaust to the frame I had the third cat removed. Even then it was much louder than it was without the third cat, very noticeably so. Point being, I can't even imagine how obnoxious a 4.0 would be with a straight pipe.

However, no argument there. It was definitely even louder after they did their work to it.
 
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The cats certainly do act as a muffler of sorts, alone they make the noise within (or near) safe decibels.

Unless your cats have gone bad, there's really no performance to be found. If that's your concern remove your exhaust and look down the pipe, they should look honeycombed.
 
I can't think of any possible situation where a straight piped Jeep 4.0 would be desirable in any way...and I'm really trying to come up with one. :unsure:
 
Actually, before they even mounted that exhaust to the frame I had the third cat removed. Even then it was much louder than it was without the third cat, very noticeably so. Point being, I can't even imagine how obnoxious a 4.0 would be with a straight pipe.

However, no argument there. It was definitely even louder after they did their work to it.
My TJ on 40's is straight piped all the way out to the rear bumper and it is only just tolerable.
 
I have no muffler behind the last cat - basically where you unbolt it underneath behind the skid plate. I actually think it sounds really good - but I need to fab a pipe to get it all the way ou the back so fumes don’t build up. Of course, prerunning and header only 350s is my background so the louder the better lol I’ll post a video here for you to see...and yes a mid arm is in the works and I bent the crap out of my stock muffler on a rock so I did have a reason!
 
Read post #12 and then read post #14

I've already read both of them, and I'm not sure why a straight pipe would add power to a Jeep 4.0. I'm not an authority on that engine, but I just don't see that the normal benefits of a straight exhaust would apply, here. I mean, there's only so much air that can go through the head...