88 Xj Exhaust Questions - Material and Flow

[RAVC1]

I need a new system including cat and downpipe. Some of what I need to know is contained here:

http://naxja.org/forum/showthread.php?t=1114938&highlight=exhaust

Yet, I need to go further into the details. Most of my Xj's have been this same vintage (i.e., Renix) so, I have history with these. Here are my concerns:

1 - Prefer stainless for quality & longevity. Seems like my only choice would be custom because, I cannot locate a full system from any after market company.

2 - The current design for the down pipe is wrong. Everything I see (as well as one I have owned) features the "hill" at the transmission cross member to prevent the down pipe from grounding against the cross member. Years ago, the down pipes did not feature this elevation change and I never experienced any incidence of contact between the down pipe and the cross member. You just have to use the exhaust flange bracket for the down pipe/CAT interface that fits into the cross member.

3 - My current cat has holes in the welds on each side. These have resulted in an increase in my fuel economy that I would like to keep. Does anyone make a high-flow cat for the Xj? Presumably, some of the stroker people can answer this question.

4 - I am willing to change the exhaust manifold if necessary but, I would need to be certain the benefit exists.

Help if you can..

 

[Johnnie Walker]

performance-curve.com should have most of what you need. A custom downpipe is probably required.

 

[RAVC1]

Unfortunately, all of their Xj systems are described as aluminized. Worse, most of the systems I have found that are stainless are made of 409 rather than 304 so, they will be prone to rusting.

 

[cal]

how long do you plan to keep the car that you're worried about the exhaust rusting out? 409 stainless or even aluminized exhaust should last you 15+ years..?

There are many companies who make hi-flow cats. I run a Magnaflow.

Upgraded headers make a HUGE difference if you push higher RPM's. Under 3500 or so not so much.

Borla made an excellent renix header with 2.5" non crimped downpipe. Its discontinued but see if you can track one down.

 

[RAVC1]

While 304 may be more desirable, I think I also have to regard it as "unobtanium" unless I want to fabricate the entire exhaust. I think this would mean an exhaust worth more than my car...

What about the Magnaflow 15856 for the 96 and newer Xj?

http://www.magnaflow.com/02product/shopexd.asp?zone=all&id=9491

If this fits it should be a good solution (costs though!).

Are any of you using one of the spun cat's? How did you size it effectively?

 

[yossarian19]

You are over thinking this.
Get aluminized or stainless and paint it with something if you need to.
Your exhaust leak is probably not an asset, don't worry about fixing it. If your cat is hurting your fuel economy, it's because you have a bad (plugged) cat.
The current design for the down pipe might be different, but if you take your bucket to an exhaust shop they will make it work (or build something that does)

 

[Johnnie Walker]

If you are going to pay high dollar for aftermarket cat-back system, Gibson and Borla I beleive make 304 stainless systems. Otherwise, basically as sated above, pick parts you want set it up and get some high temp paint.