I replaced my banks header today. In doing so I got to looking at the downpipe and its dent. Now I know a billion folks have asked if this is restrictive and that it was a factory added bend for emissions purposes.

What Ide like to know the truth of is, does replacing this dent with clean tube aide in a reduction of torque and/or power loss via lack of backpressure, or would it actually gain some power/torque.

I know with the new header I'm getting a little further into the seat which is cool, now I'm curious if there's any reason not remove the dent?

 

You ever see those dents in airplane, harley or race car exhausts ?

Me neither.

 

a bigger exhaust on these XJ gains power, the stock exhaust is too restrictive

I have 3 x '96 with stock, 2" with headers and 2-1/2" with headers

 

It's my understanding that a dent in an exhaust pipe crushes one side (we'll say north/south in terms of cross section diameter) while the other sides (east/west) spread apart. The resulting oval shape is very similar in diameter and air flow volume.

I hope I explained this ok, anyway you shouldn't lose or gain a noticeable amount power with or without dented pipes.

On a side note, my downpipe is dented in a very similar area. Although, in my case the dent is very close to the flange at the header, and I believe the flange itself is out of round causing an exhaust leak. I will be replacing mine soon to see if it cures the leak, I would suggest you replace yours if it's causing an exhaust leak.
​

 

I don't see the same volume getting through this but I don't know jack. My eye says it looks wrong.

 

From my buddy at JeepTech back in the day.

The "crush" in the pipe was to restrict the flow, make it hotter, so the catalytic converter began working sooner in the EPA driving test.
It appears to be there to make clearance for the front driveshaft.
Take a gander where the exhaust pipe goes over the trans crossmember....same thing.

 

One time this was discussed, someone that knows says this exhaust restriction is to heat the Cat quicker due to emissions concerns, no other reason

I can see no other plausible explanation to crush the pipe there

The XJ has a small exhaust diameter for such an engine as it is, without that

 

That was most likely me....LOL

 

It probably was, and that picture shows why you can feel a distinct difference in power with a bigger exhaust

I'm not a big fan off large exhaust systems normally, probably just doing away with crush section would be a good move

a 1.5 Litre engine would have that exhaust

mine uses a bit more fuel than I think it ought, and that may be due to a larger exhaust

 

Yeah, that does look like a fairly considerable dent and is probably restricting flow as mentioned above. Although, without inner diameter measurements who could be sure.

I saw this a while back and thought it was pretty interesting.
https://www.dailymotion.com/video/x3vupq0

 

Have any of you removed this dent?
Did it effect mpg at all?

I did see another episode where they changed exhaust 2-3" and had significant HP gain. If I was to take this dent out I think I would make everything 2.5" at least.

 

I haven't fixed mine yet. I also thought about going to 2.5 and decided against it on account of hearing somewhere (probably this forum) with less back pressure form 2.5 the gases move too quickly for the O2 sensors to collect accurate data and can cause some issues. I instead, decided to go with a header and magnaflow high flow cat and muffler for a little better flow without accidental overkill. I have the header and cat in but need to add the muffler and all new pipes when I can afford it.

EDIT: I know a lot of people here have gone to 2.5 and I don't think they had many issues. Maybe someone with 2.5 can educate us.

I hope this helps.

 

I replaced my down pipe without the dent, and it seems to breath better at higher rpms, and I had no problems passing smog test

 

do you think youve lost any bottom end torque?

 

What is bizarre to me is how much knowledge exists around the Jeep Cherokee XJ, and every single XJ in America came with this Dent from the factory, yet somehow nobody really seems to understand what it was for.

How can that possibly be. I wonder if anyone has tried to track down somebody that worked at one of the plants back in the day.

I'm in the same position as the OP. I think I am going to leave it. There are a number of reasons people have cited why it could possibly be there some relating to engine performance, others relating to emissions or clearance.

The fact is nobody really knows.

But it stands to reason that if they did it to every XJ they produced, they sure as heck did it for an important reason.

So until someone figures it out or dinos it out I'm going to leave it.

There are many "upgrades" that seems to be really common among jeepers... that down the road we find negatively impact other areas of performance in an unanticipated way. The people that knew this vehicle better than anyone on the planet, designed it that way. I fear changing things sometimes has unintended consequences in other areas, even if you see an increase in performance you were looking for.