exhaust downpipe

Hasta Yeah, yeah yeah...I know.

I tried having a exhaust shop do a custom 2.5 exhaust from the collector back and it did not turn out well. After several returns to the shop due to leaking and hitting I'm looking for something different. My searches have turned up only Walker, and Borla (if I buy their header) What other options do I have? Another shop recommended buying something bolt on and going from there...well ?

I went with a replacement Walker downpipe,which is NOT mandrel bent,but was more open than the twice dented factory pipe.
I have know idea if a pipe is available from the dealer or if the dent is missing in a dealer item.
Mine goes to a Walker direct fit cat and a Dynomax cat back system(which is also a Walker part).
I have no rattles or leaks,but it does hang lower under the motor...
Its also on an APN header....

go to a better exhaust shop?

Wayne Sihler said:

I went with a replacement Walker downpipe,which is NOT mandrel bent,but was more open than the twice dented factory pipe.
I have know idea if a pipe is available from the dealer or if the dent is missing in a dealer item.
Mine goes to a Walker direct fit cat and a Dynomax cat back system(which is also a Walker part).
I have no rattles or leaks,but it does hang lower under the motor...
Its also on an APN header....

Click to expand...

I have an uninstalled APN (actually an API w/ same part number) aftermarket header, for a 98 XJ ...

Currently the 98 XJ Federal exhaust .. does not have an OE cross-over pipe with a dimple (dent), that is installed with a leaky OE exhaust manifold. My fuel economy has fallen from 18-19 mpg (average) to around 14-15 mpg (average)

After finding some old posts from 2005 on another forum. The discussions shows, according the several people and posts, that the dent was put there by the OEM for a purpose i.e. to provide 1 to 2 psi back pressure for the 4.0L engine in order to improve the performance and fuel economy at lower rpms.

One person stated that for the stock OE exhaust a straight down pipe would only improve performance in the 4500+ rpm range.

** I could not find any more information about the front pipe for the XJ other than some aftermarkets may have a dimple while others do not, some may have crushed tubing while others are like the OE, others may be either stainless or aluminized and mandrel bent.

Most cat-back systems should work Ok with any type of exhaust system (OE vs performance)

__________

_ Other things to note: the original OE exhaust used a 1. the old style cat. conv. with pellets 2. was mandrel bent 3. stainless steel, 4. used a more restrictive OE muffler and was 5. 2.25 inch throughout.

_ At one time Jeep offered an optional performance exhaust .. options included 1. a performance header and/or 2. a catback system (a performance muffler with a 2.5 inch tailpipe) there may have been a different intake however .. I don't remember ever seeing a modified intake for that time period ...

_ in 99-00 other changes were made to the OE exhaust system ... some changes were made to the header and/or intake (larger streamlined intake and modified two part header, etc.) ... I think to offer improved economy and performance (hp) and to meet certain EPA fuel economy and emission standards (sometime after 99 there were a couple of pre-mini-cats for some XJs that were added to meet Calif. emissions.)

FWIW, I don't believe that bit about the dent being for performance. I seriously doubt they'd have used a larger pipe and crushed it, for backpressure, in the exact same place the front driveshaft smashes a pipe without the dent in it.

hubs97xj said:

FWIW, I don't believe that bit about the dent being for performance. I seriously doubt they'd have used a larger pipe and crushed it, for backpressure, in the exact same place the front driveshaft smashes a pipe without the dent in it.

Click to expand...

I think so too ... but anything these days is possible ... my first car was a 56 chev, fairly straight forward, no computers ... pretty much warned you before something was about to break or wear out.

I haven't figure out the leaky exhaust manifold, other than it needs to be replaced ... it may have an effect on the o2 sensor i/o? my fuel economy sucks .. I read a while back about how the computers (pcm) logic and circuits work with the o2 sensor setting fuel trims, etc. but haven't really determine how much of an effect the exhaust directly or indirectly has on the computers ..

One point I think is the performance exhaust may behave differently than your stock and have a effect on a vehicles drive-ability ... if you change one part of the exhaust and/or intake without modifying another the results may be less than predictable.

hubs97xj said:

FWIW, I don't believe that bit about the dent being for performance. I seriously doubt they'd have used a larger pipe and crushed it, for backpressure, in the exact same place the front driveshaft smashes a pipe without the dent in it.

Click to expand...

It's certainly not there for performance. It's there for emissions. Slow down the exhaust and heat up the cat sooner. Routed by the factory to appear that the "crush" is for driveshaft clearance.

Straight from a buddy of mine at JeepTech who worked with certifying the 4.0 for emissions with the EPA.

Re-route the pipe and without the crush and feel the power difference. done it numerous times. Good guy at a muffler shop can do it easily.

At stock height is the only time clearance for the shaft is an issue. 3" of lift and you could route the pipe in the same configuration with no worries.

I heated the down pipe up cherry red and worked the bump out. I'm at stock height and have no rubbing issues. I felt a seat of the pants gain, but didn't drop it on a dyno.

My son went to Ledzema muffler shop in Chula Vista for his 4.0 swap into an Eagle wagon to have a down pipe made. It had to make some weird twists to get around the clutch slave cylinder and bell housing, so a good muffler shop can work wonders.

cruiser54 said:

It's certainly not there for performance. It's there for emissions. Slow down the exhaust and heat up the cat sooner. Routed by the factory to appear that the "crush" is for driveshaft clearance.

Straight from a buddy of mine at JeepTech who worked with certifying the 4.0 for emissions with the EPA.

Re-route the pipe and without the crush and feel the power difference. done it numerous times. Good guy at a muffler shop can do it easily.

At stock height is the only time clearance for the shaft is an issue. 3" of lift and you could route the pipe in the same configuration with no worries.

Click to expand...

Some older vehicles used an exhaust valve to pre-heat the engine and possibly devices such as the EGR valve, etc.

and can visualize how a dent might be used slow down the exhaust a bit so the o2 sensors can work more efficiently .. providing better feedback allowing the PCM to adjust fuel trims more effectively ..

If what the Jeeptech said is true ... perhaps the engineers were trying to meet certain emission standards while trying to adapt emissions to an earlier engine design, etc. ...

[
If what the Jeeptech said is true ... perhaps the engineers were trying to meet certain emission standards and while trying to adapt emissions to an earlier engine design, etc. I would wonder how many XJ's came from the factory with this sort of exhaust restriction so the emissions could function properly.[/QUOTE]

That's exactly what they did. And, I'm pretty sure all of them had it, even the 2wds.

Yes the 2wds have them--I banged my brother's 93 2wd down-pipe out when it was red-hot and my 96 had one too. I even think the 88 2wd Eliminator has it too. Why make an un-crushed down-pipe for <10% of the XJ line?

cruiser54 said:

It's certainly not there for performance. It's there for emissions. Slow down the exhaust and heat up the cat sooner. Routed by the factory to appear that the "crush" is for driveshaft clearance.

Straight from a buddy of mine at JeepTech who worked with certifying the 4.0 for emissions with the EPA.

Re-route the pipe and without the crush and feel the power difference. done it numerous times. Good guy at a muffler shop can do it easily.

At stock height is the only time clearance for the shaft is an issue. 3" of lift and you could route the pipe in the same configuration with no worries.

Click to expand...

Bringing this back from the dead here. I had my exhaust guy install a 2.5" full mandrel bend post header back. However I'm not lifted yet. I am defiantly rubbing the front drive line under heavy breaking and mid/minor bumps. I'm almost considering about going with a smaller diameter. I'm worried that with the 2.5", I'll even rub it when I'm at full flex (even while bump properly stopped) on the driver side. I'm planning on 3.5-4.5" lift either 31-32's. I mean I know the bigger tires will help with not getting as much up travel as stock. Just want to be 100% sure.

The routing of the pipe is very important. It must be tucked up, unlike the original.