I have a 1998 XJ/4.0/automatic/4x4. The connection between the muffler and cat rusted out, and, when I took a corner too hard the muffler fell off. Now it sounds like a broken UPS truck...

I was planning on reusing my stock tailpipe until some idiot stole it. I'd like to use this opportunity to upgrade the exhaust a little bit, but I don't want to spend a whole lot. I already have a 2.5" Flowmaster muffler that I want to use. (leftover from another project I never finished) I might as well get a 2.5" tailpipe to go with it.

Now I'm interested in replacing the front pipe and getting rid of that stupid pinch right after the exhaust manifold. From searching, it sounds like people who have used aftermarket pipes without the pinch end up hitting it with their driveshaft, causing damage. Other people seem to have no issue with this. On a completely stock XJ is this going to be a problem? I'm not going to be doing much offroading or flexing. The cheap Walker replacement pipe does not have the pinch, and I've read both good and bad things about it.

Additionally, I read somewhere that an exhaust shop might be able to remove the pinch without replacing the pipe. Is this true? Again, I'm trying to keep this as cheap as possible. I want to do the work myself, but I would let a shop remove the pinch if I can.

 

I'd talk to a shop about removing the pinch or fabbing a new downpipe. I'd expect it possible to have it done for as much as the Walker downpipe costs or less. I mean, if you don't like the shop's quoted price, you can always decline and go with the Walker pipe.

I had a driveshaft-exhaust collision with mine, but I'm using a Thorley header and fabbed downpipe that wasn't fabbed well enough to avoid that problem in the first place.

Explain to the shop until you're blue in the face that the driveshaft CAN collide with the downpipe if not routed correctly. I'm not sure if this IS possible with the stock header and stock routing, but it is definitely possible in some situations such as my own. I thought I was clear with my shop, and he doubted me the whole way. When I questioned the situation when I picked it up, he insisted there was no way they'd hit each other. I drove to the end of his parking lot, hit the brakes, and BRBRBBRBRPRPPBRB!!!!! The best way is to hit the brakes AND turn right. If it doesn't hit in that scenario, it will never hit.

 

you need the dimple to clear the pinion for hp30's which your 98 has.

 

I recently had a shop do a 2.5" exhaust from the header back, including a fabbed down pipe, magnaflow cat, flowmaster muffler, and tailpipe.

I have not had any issues with the down pipe and exhaust trying to occupy the same space. Haven't done much wheelin since getting this set-up though.

I would not recommend doing 2.5" all the way out. I definitely lost some low-end torque from freeing the exhaust up that much. I currently have a stock intake that is waiting to be replaced by a Spectre cowl intake. I'm hoping the intake will get me some torque back down low.

In your situation I would run 2.5" to the muffler into a 2.25" tailpipe. I think a 2.25" muffler would be better but no sense in getting a new muffler over a 1/4".

 

I agree completely. I did 2.25" the whole way because my header collects to 2.25, and I didn't feel like getting even more creative, but ideally I'd have don't 2.5 to the cat/muffler and 2.25 out the back.

You specifically, XJlim, might want to combine a bored throttle body with that cowl intake. Ideally a ported and polished head would also happen, but at least eliminate any bottle-necking of airflow that the TB might cause. Ya know, or just do a 2.25" tailpipe since it's not like XJ tailpipes are expensive pieces.

 

See, this is why I had to ask. Apparently you need the pinch, and you don't...

As far as the OEM exhaust goes, I think this is a terrible design. Maybe it's for emissions or something, but, even if the dimple on one side is for the driveshaft, then why is the other side smashed too? And why is the first section of pipe a smaller diameter than even 2.25"?

The walker pipe has no dimples and is supposed to be an OEM replacement for any stock XJ, I know that might not exactly be true, but apparently they didn't get the memo about the need for a pinch there. It's got terrible crinkle bends, but, still probably flows better than OEM. I can't imagine every one they sell causes interference problems.

As for the tailpipe, I don't think it matters how large I go. Right now I'm driving it around with the exhaust ending at the cat, no muffler, no tailpipe, and I notice no loss of torque. I would just add a downturn there and leave it at that, but I need to pass an inspection in a few months.

I plan on keeping my OEM cat, (if I can get it off) but I'd really like to feed it with at least an unpinched 2.25" pipe.

Does anybody know if the pinch can somehow be removed from the stock pipe by an exhaust shop? I read an article about that somewhere a while ago, but now I can't find it. Is there some way for them to pop the dent out?

I hesitate to let a shop touch my Jeep for any reason, not because of the cost, but because I've been screwed on automotive work way too many times. If you want it done right you usually have to do it yourself.

I'm not looking for huge performance gains, though I will upgrade the air filter and throttle body in the near future.

 

The pinch isn't for clearance, the pinch (which is towards the top of the pipe not really the drive shaft side) is to help heat the oxygen sensor and they claim the catalyst up by redirecting the exhaust gases,faster that these heat up the faster the ECM can go to closed loop. strictly for emissions purposes. if you have a pinch on the other side then something hit it. You wont notice much of a difference on a stock XJ by leaving it there. You need to seriously step up the flow game before that pinch causes any real problems. And if you are running a stock exhaust manifold then a pinch in the down pipe isn't your biggest restriction source., wait until you get headers then have a custom pipe made from there. Problem with walker products (and i do use them but just saying...) is they dont last as long as OE at least in the salt belt. They rust up like crazy and usually rot out in 2 or 3 years which is why i'm suggesting just save it until you do the headers and have one made then.



As for going to a shop for work, yes there are shops that rip people off. Just like there are salesman who rip people off, just like there are doctors who rip people off, governments that rip people off... untrustworthy people are every where, it takes some due diligence to find the honest ones. Not all shops are the same.... and it's hard to do the job right if you don't have the specialty tools needed in order to do it right. most people aren't going to buy a mandrel bender for one exhaust job, or even for that matter to have the space to store it. however i always promote working on your own jeep if you have the ability, tools, and know how for work arounds.
This should be the pinch

 

I'll have to respectfully disagree with that. I have no interest in ever getting headers for my XJ, the stock "manifold" is actually a pretty good design, much more like headers than many other vehicles might come with from the factory. Also I don't have that pre-cat BS that the newer ones have. I know the '98 has a better OEM manifold than some of the earlier years. Maybe if I was building a stroker or something, but that ain't gonna happen.

The amount of backpressure in your exhaust is a sum of all the restrictive points. Removing one, even while leaving another, reduces the overall restriction. I realize some restriction is necessary on a mostly stock vehicle or you will lose low end torque, but the factory manifold and cat should be enough to provide this.

No, I don't "need" to remove the pinch, but since I'm working on the exhaust now it seems like a good time to do it. I'd also like to wrap the front pipe with insulation due to it's proximity to the oil pan and torque converter, this would probably also help to heat up the cat and O2 sensor. I'd also like to put some sort of heat shield between the exhaust manifold and the intake manifold, and will probably install a '99+ style intake at some point. The combination of a better air filter, larger throttle body, and newer intake manifold will increase the amount of airflow into the engine. I won't likely take it any farther than that.

Really I'm more interested in improving gas mileage than horsepower, but I know this is a controversial topic and I don't want to discuss that here.


....but the question still remains, can a competent exhaust shop simply pop the dent out of the stock pipe? I'd rather keep the OEM pipe than replace it with something else.

 

any full service shop with an oxy acetylene torch should be able to pop it out. if you bring them the pipe yourself might take any where from 10 minutes to a half hour in labor probably. if the pipe is still on the car I imagine a shop my charge any where from an hour to 1.2 hours to r&r.

 

I did a lot of research on the 2.5" vs 2.25" debate before deciding and didn't really find anybody that regretted going to 2.5" so I went for it. Fingers crossed that the intake does its job. I'm not sold on bigger throttle bodies. From my understand it seems that they will only allow greater airflow at WOT. Other than that the flow is still being restricted by the butterfly. Bigger is not better in the intake/exhaust department. When looking for torque and gas mileage its all about flow velocity, not volume. Lets all remember that formula from physics class, (Area1)(Volume1)=(Area2)(Volume2). As the cross sectional area goes up, velocity goes down.

As was said before, I believe the pinch is there for emissions reasons. I felt good replacing that.

I don't know how you put up with the exhaust dumping under the rig. I always found it drones horribly without a tailpipe because the exhaust just echos off the bottom of the rig and the ground.

I've never heard of somebody popping that pinch out without replacing it. Sounds like more work than its worth. Just put new pipe there.

 

The larger TB isn't actually about raw flow. That's what a lot of people think, but not me. See, the trick is, and this isn't always important/useful which is why I don't bother having a bored TB, is that a larger TB can flow the same amount of air as a stock TB with less throttle. I'm not expert enough to know if this ultimately matters or not what with the computer still being the ultimate authority, but it is an intriguing notion.

I'm aware of most people's tendency to obsess over a misconceived notion of flow and not grasp the importance of velocity. Exhaust gas velocity is why I've kept a 2.25" pipe on my 4.0 and why I'd have ideally started at 2.5" and reduced to 2.25" because as the gases cool in the system, they get denser.

Ultimately this is all MAJOR hair-splitting, however, but isn't that what these forums end-up being about so often now that it has been 16 years since the last XJ and even, what, 11 years since the last 4.0 was in a Jeep from the factory? Nothing left to learn after all this time except perhaps what might be discovered after a hair has been split.

 

Honestly, with the windows up I don't find it that loud. Yeah, there's a drone, but it doesn't bother me too much. It's amazing how much sound the cat eats. I would at least put my flowmaster muffler on there, but, if I didn't have to pass an inspection I'd probably just delete the tailpipe. Me and the 4.0 have a long history, I guess I'm just used to that very specific sound.

Only reason I'd want to keep the stock pipe is because I know it fits right, especially with the stock cat I'm keeping. The Walker pipe is supposed to be a direct replacement, but, that isn't always the case with aftermarket stuff. Not sure if I want to have a whole new pipe fabbed, but if I did it would be 2.25" all the way instead of that 2" or whatever section at the very front...

As for the TB, I think part of the trick there is just getting rid of that lip on the inside under the throttle plate. It can't be good for velocity, probably more emissions crap.

I appreciate the information everyone.