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Catalytic Converter & Header


 
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DavidXJ
Member


Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Mon Nov 12, 2007 12:22 pm    Post subject: Catalytic Converter & Header Reply with quote

I am planning on putting on a set of Pacesetter headers, a Spin Tech muffler and a Spin Tech catalytic converter on my 1998 Cherokee Classic 4x4, 4.0L (I absolutely destroyed my exist. system running the Dusy Ershim w/ only 30" tires). But the headers have two choices... with warm-up cat. or without warm-up cat. I have no idea. The only reason I am even dealing with the exhaust myself is because I have to in order to be able to afford this install. Exhaust is not one of the wrenching jobs I look forward too.

So, what is the difference between a warm-up cat. or a non warm-up cat.?

How can I determine which of the two systems I have?

Last, what is a good exhaust pipe diameter for a 4.0L exhaust system? I know Rusty's sells a tailpipe that is 2.5", and I can get the muffler and cat from Spin Tech in whatever size I want. But I can't find any info on the diameters for the pipe from the header to the cat or any info on the outlet size of the pacesetter header.

I have read somewhere that it would be best to slow reduce the diameter of the pipe to end up with 2.25" at the tailpipe. Is this bogus, or is the Rusty's 2.5" tailpipe, 2.5" cat and 2.5" muffler going to cause resonance and loss of lower end torque?

Please don't just tell me to buy such and such a complete system, because unless it comes with a good header, high-flow heavy duty cat, high quality muffler and tailpipe for under $600, it will be cheaper for me to by these parts separately like I intend to. I am mainly looking for advise on pipe diameters and that whole cat. converter thing.

Oh, and I'm being verbose, but how in the world do you protect your exhaust system from being devestated by the rocks? I can protect everything else with sliders, rocker protection, bumpers etc,, but the exhaust just sort of hangs there. Any ideas or experience with this?
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bajafanatic
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Joined: 27 Jul 2007

PostPosted: Sat Nov 17, 2007 4:01 pm    Post subject: Reply with quote

You can fab some skid plates for protection....

As for knowing which type of cat you have.. look under your XJ where the pipe comes down and goes under the oil pan... if it swells out right there.. you have a warm up... if it does not, you don't.
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DavidXJ
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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Wed Nov 21, 2007 7:48 am    Post subject: Reply with quote

Crap... I have a warm-up cat. Our local muffler shop convinced me not to go with the Pacesetter headers due to quality issues.

So I have now purchased a set of Banks headers and Rusty's Flowmaster/tailpipe set. I went with the Banks because they seem to have the quality, and as far as I can tell, I can utilize my existing &*^%!! warm-up downpipe and catalytic converter. For now this will have to do.

But, in the future, is it possible for a muffler shop to make a new downpipe with a "warm-up cat" bulge in it? I wouldn't mind sticking with the stock down pipe except that it necks from what seems like 2.5" down to something like 1.25" and then back to 2.25" before that cat. What are my options with this downpipe?
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ehall
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Joined: 21 Jul 2007

PostPosted: Wed Nov 21, 2007 8:14 am    Post subject: Reply with quote

Your muffler shop should be able to tell you the pros and cons of changing diameter. Generally speaking most people like to keep it normal for simplicity--you can end up with a lot of gurgling noises with custom exhausts, and it will be really hard to diagnose if your design is too complicated.
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