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Author Topic: Late model 4.0 exhaust  (Read 3917 times)

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Offline Zoro

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Late model 4.0 exhaust
« on: September 29, 2018, 02:16:36 AM »
I've got a 4.0 from a 2003 Wrangler I'll be swapping into my Eagle and I'm trying to figure out the exhaust. I see there is a gorgeous header out there for the 4.0 head in the Eagle BUT I believe it's designed to have the CAT after the header. On the model of 4.0 I'm using there are 2 CATs that each collect from 3 cylinders before the Y pipe.

Is there a header out there that would accommodate my setup? My goal is to have the 4.0 running in the car as if it were stock and emission legal.
84 Eagle Wagon aka 'Zoro II'
263,000 miles and counting!

Offline vangremlin

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Re: Late model 4.0 exhaust
« Reply #1 on: September 30, 2018, 08:07:59 AM »
I have a"header" style exhaust manifold that is hooked up to my 4.0 head, came out of a mid 90s Jeep, and the cat is farther back in the exhaust train.  Not sure what came in the 2003 Jeep but adding the cats in before the "Y" sure would make things crowded in there lol.  Hope what you're looking for exists.
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline Zoro

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Re: Late model 4.0 exhaust
« Reply #2 on: September 30, 2018, 11:35:15 AM »
The 2003 is weird, has 3 cats. 3 cylinders per cat on the first 2 then one farther back
84 Eagle Wagon aka 'Zoro II'
263,000 miles and counting!

Offline The Dark Side of Will

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Re: Late model 4.0 exhaust
« Reply #3 on: December 15, 2018, 07:17:47 PM »
Here's the 2003 cat & downpipe:

The '03 manifold is split into two sections. Each pup-cat serves 3 cylinders. Since the pipes wrap around the front of the sump, this exhaust is incompatible with the Eagle front diff, which needs to occupy the same volume.

Get an older single outlet manifold and down pipe. That will easily work in an Eagle. Here's how my swap is going:

As noted previously in this thread, the diff snout bracket is the only part that needs to be made in order to do a 4.0 swap.

My initial takes on it ended up with very minimal clearance to the stock 4.0 manifold and stock Cherokee downpipe that I have.

I finally had a realization of a simple change I could make that would dramatically increase clearance to the downpipe.


Here's how it fits to the downpipe:

Here's how the downpipe fits around the engine and transmission:

And how it clears the bellhousing:

« Last Edit: December 15, 2018, 07:18:45 PM by The Dark Side of Will »


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