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Old 01-01-2014, 09:44 AM
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krazy kyle's Avatar
Join Date: Jul 2012
Location: battle mountain, NV
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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

'93 Black YJ, 4.0L AX15 - UNDER CONSTRUCTION! https://www.wranglerforum.com/f330/2x...ad-490865.html
Old Jeep that was totaled (and SOLD!): https://www.wranglerforum.com/f330/2x...ad-101879.html
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Old 02-01-2015, 07:13 PM   #4
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Location: Eastern North Carolina
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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.
90 YJ, Laredo on 33-12.50x15, Pro Comp Xtreme A/Ts with 3.55 gears......... Building first 4.6 stroker.........

....Just JUMP, and build your Wings on the way down....
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