• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

This cannot be right - down tube

H

highhilleer

NAXJA Forum User
Location
West Virginia
What's the proper name for the tube that goes from the exhaust manifold to the cat. I've heard down tube, front pipe and J tube? Anyway I went under the Cherokee (97 SE) today and found this. :(
frontpipe.jpg

I know this tube was not made with a mandrel bender, but should there be a big flat place near the manifold connection???
I tried to look at a replacement pipe at Advanced Auto, but it is NA on their computer. I could not find one on the internet. Is there a source for replacement or better down tubes?
I then put the eye on the cat.

cat.JPG


I think the whole bottom of the cat should have that cover with the holes on it? Opportunity to install a high flow cat? Recommendations? Aren't manufactures required to warrenty cats for a certain period? This Cherokee has less than 28,000 miles even though it is 7 years old.

Moving on to the muffler.

muffler.JPG


The outer cover is peeling away.

Looks like that Rusty's cat back system has become close to a need rather than a want!!! :)

TIA for your input.
 
Last edited:
That bend is normal and has no effect on how your XJ runs.The cat should have that shield but unless the innards of the cat are bad it won,t be replaced under warrenty(80 K) on emissions stuff.
A cat back system would be a cost effective thing to do.
But heck your from West By-God Va,and I,m sure you don,t want to look out of place with a new exhaust. :)
Wayne
 
Yeah I thought the same thing when I looked at the down tube! I checked my freinds two XJ's and they had em too!
The cat is a piece of Junk pull that sheild off and trash it! I did the same thing and also my cat insides were all broken up. It made a bad noise when I started the jeep, until the softball sized peice of the broken up cat got stuck in the out tube. I have passed two emissions test with out it and it sounds so much better! I did price a new cat and it was over $300. So if I ever have trouble passing emissions I am going to the pick and Pull!
Hope my info helps!
 
Wayne Sihler said:
That bend is normal and has no effect on how your XJ runs.The cat should have that shield but unless the innards of the cat are bad it won,t be replaced under warrenty(80 K) on emissions stuff.
A cat back system would be a cost effective thing to do.
But heck your from West By-God Va,and I,m sure you don,t want to look out of place with a new exhaust. :)
Wayne
Click to expand...
I have to believe the reduction of cross section must inhibit flow, and therefore power, even if it came from the factory that way. But I won't worry about if for now.

I'm from VA originally, so I carefully reviewed local customs. A new exhaust is OK as long as it makes the vehicle louder! :)
 
Ok, through a search of the site I came up with this picture by MJR:
orig.jpg

Clearly the pipe was manufactured with a "dent". Is there any possible reason for this dent? Create a little back pressure? Ease manufacturing? Any ideas? On Dr. Dyno's page, http://www.jeep4.0performance.4mg.com/diary.html, he states modifying the "S pipe" (another term?) provided great improvement and replacing the stock manifold and modified S pipe with a Borla header only netted about 5 hp. Hence my interest in this subject.
 
that indentation is for front pinion clearance.. (at least thats what i deduced) i never realized how close it was before... now that it is lifted and i flex the passenger side whel up into the fender well the pinion yoke is actually pulled close enough to the pipe that it took a few wheeling trips to "self dimple" the spot so it didnt make contact anymore.. i know some have actually had the yoke tear a hole in the pipe.... the indentation on the pipes in my 87 and 99 are a litle different too.. so i may be totally off on my theory but it works for me...
 
Atom said:
Yeah I thought the same thing when I looked at the down tube! I checked my freinds two XJ's and they had em too!
The cat is a piece of Junk pull that sheild off and trash it! I did the same thing and also my cat insides were all broken up. It made a bad noise when I started the jeep, until the softball sized peice of the broken up cat got stuck in the out tube. I have passed two emissions test with out it and it sounds so much better! I did price a new cat and it was over $300. So if I ever have trouble passing emissions I am going to the pick and Pull!
Hope my info helps!
Click to expand...


You wont find them in the Pick and Pull. Cats are considered, by the EPA, as a hazardous material.

You will have to buy one new...
 
new cats at Summit Racing for 100$

my '88 has that dent as well...mostly due to the yoke hitting under hard compression/flexing. maby this is why so many Xj manifolds crack.
 
sidriptide said:
that indentation is for front pinion clearance.. ... the indentation on the pipes in my 87 and 99 are a litle different too.. so i may be totally off on my theory but it works for me...
Click to expand...

Am I understanding you correctly? The dents in the down tube are the result of impact with the suspension? Would a highway vehicle ever need enough suspension travel to cause this type of dent? You do not think the tube came this way from the factory?
I sure would like to see a replacement tube to see if they have indents, but I haven't been able to find anything on the internet.
Thanks for your input.
 
My dealer said that dent is there to tune the exhaust to help it run more effectively and more smoothly through the system. Apparently the crimped tube helps to retain a particular harmonic resonance in the pattern of exhaust air moving through it. On the other hand, I have not seen a similar crimp on TJ's with the same engine, so go figure.
 
It is definitely my theory that it is there for yoke/driveshaft clearance, if you go look underneath your xj, look how much uptravel is left in the springs, then just imagine how close that pipe will be to your pinion when fully compressed
 
I too vote for the yoke/driveshaft clearance theory. Although mine is dimpled for what I beleive to be clearance, my yoke is still beating the crap out of my exhaust right there. It's only a matter of time before it tears a hole...

-jm
 
you could try to jack it up, but the only way to tell for sure is to observe the axle under full compression, which will be much different than full articulation, as far as where the driveshaft is, and this is a dificult thing to see, unless you are willing to do something drastic like remove your springs and then jack up the front axle
 
full compression will bring the axle straight up and a little closer to the pipe, but flexing the right side up will pull the axle a little more.. unless you jump your XJ you will hardly ever see full equal compression, but i guess a good dip onthe highway will do it too.. it may be for tuning purposes but i think its close proximity to the active suspension it is more likely for clearance... i never had contact issues until i lifted my 87.. and my 99 with a small lift has not had any issues at all.
 
You must log in or register to reply here.

Similar threads

N
problem removing transmission pan
Replies
17
Views
3K
techno1154
techno1154
M
Need Part Number for Drum Brake Wheel Cylinder Dana 44 Axle
Replies
2
Views
76
Bent
Bent
XJJeeper59
99 XJ ECU Swap Question?
Replies
2
Views
2K
XJJeeper59
XJJeeper59
L
1994 XJ 4.0 exhaust down pipe size/flange?
Replies
3
Views
2K
Lordhelemt
L
Jeepmedic46
Exhaust
Replies
2
Views
955
jeep ride
J
Back
Top