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Old 01-01-2014, 09:44 AM
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Will a 4.0 exhaust system work on a 4.2

Hi I'm asking this because I've been searching for an aftermarket performance exhaust system and I have been finding a lot of good choices for jeeps 91 and up but I have a 89 4.2 and it seem there aren't as many choices. So if you know if a 4.0 exhaust system will work or if you know of any good exhausts for my year that would be helpful to.

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Old 01-06-2014, 09:55 PM   #2
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4.0 has a different exhaust manifold dump than the 4.2. You can go to the local exhaust shop and see what they quote you to build something. Might be cheaper than you think.

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Old 01-06-2014, 10:04 PM   #3
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You looking for the pipe? or a header?

I know lots of exhaust shops who run the 4.2 exhaust around the front of the pan like on the newer 4.0L, helps ALOT with front driveshaft interference after a lift...

If you are looking for a header,

Borla Performance 17062 - BORLA T-304 Stainless Steel Header for 88-90 Jeep® Wrangler YJ with 4.2L I-6 Engine - Quadratec

Compare that to the 4.0L header setup in this link to see how it wraps around the front of the pan, THIS WILL NOT FIT THE 4.2L

https://www.quadratec.com/products/17601_06_07.htm
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Old 02-01-2015, 07:13 PM   #4
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Take a quick look at you 4.2 center exhaust flange... It has 2 bolts up top in the center... Now if you check the 4.0 you will see it only has one bolt dead center top.
The 4.2 uses a siamese 3 & 4 exhaust port where the 4.0 has individual ports.
Additionally, the head is the weak link on your system, not the pipe. Really poor flow. Find yourself a good 4.0 head to put on with a good header. You won't spend a fortune and you will be happy.
Lots of good info out there...Good Luck.
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