In doing a Gooogle search for "Jeep with Viper engine",I came across a hit that was a JP MAgazine page with suggested enigine swaps.I skipped passed the Chevy and Ford "suggestions" because I'm just old enough to be "old school".Growing up I would always run into someone who either was going to,or already had,inserted a non-AMC/Jeep engine into their CJ.This would disgust me,and make me laugh at them at the same time.Having grown up riding in,and then driving,only AMC's and Jeeps,I was more than aware of the ease of being able to bolt in a 304 or AMC360 in place of the 6 cyl,by only moving the engine brackets on the frame to their secondary predilled holes.The 258 and V8s share the came bell housing.You could start the job at sunrise and drive the thing to lunch.
 So,when I came across the following statement of fact by a JP Magazine employee,I fealt the need to subscribe to this forum and type a verbose disertation of my disgust...

"4. Jeep 4.0LWhat: Introduced in the XJ in 1988 and designed after Chrysler's 2.5L four-cylinder, the 4.0L inline-six has proven to be a torquey powerhouse with a reputation for durability."

 The 4.0L was actually released in 1987 due to a much needed replacement for the 2.8 GM V6 POS tha twas used from teh XJ's release in 1984 thru the 1986 model year.Jeep designers stuck with an old AMC mantra of reuseing a tried and true system.They ressurected the 232 I6,the previous version of the 258,and multiport fuel injected the SOB.While employed at a Jeep Dealer,I personally saw a person trade in an SS chevy pickup for an ELiminator Pickup with the 4.0l because someone had kicked his ass the day before with one.They had drag raced up the road in front of the dealership whilst many of us just happened to be outside during our lunch break.

 So if some of you find this just a little too much,I apologize.But after years of seeing incorrect info and History on AMC's and JEEP's,such as the many advertised by used car dealers here in upstate New York with V6's,which XJ's and ZJ's never came with,instead of inline 6's,I couldn't help myself.

 Tim Morris,
 I still have my first vehicle that I got when I was 12... A 1949 Willys CJ2A.I'll never get rid of it,and will be buried in it when I die.  

It is funny you should write. I actually thought the same thing when I read that a while back. I even commented to a friend about the statement. I would have said that both the 2.5 and 4.0 were versioned from the 258. Because the 2.5 came out before the 4.0, it was the inspiration? But they both share so much with the old I6s.  

Glad someone had the time to read all I wrote.I kinda got long winded there.The 4.0 was the 4th incarnation of the venereable AMC 6 cyl.1st was the 232 which came in in 1964.In 1966 they downsized it slightly to 199 to replace the old Nash 196.In 1970 they dropped the 199 for the 258 by raising the deckhieght slightly and retaining the longer 199 connecting rods.All 3 were essentially the same block.The 4.0 was released in 1987,a 232 basically bored up to 242CI.This is why guys who put the FI kit on their 258s have more power than someone with a stock 4.0 'cause the 258 has a longer stroke.Put all 4 bare blocks,199,232,258,and 4.0l(242) next to eachother on an engine stand and you'd be hardpressed to tell which was which.

 The 2.5L is in fact a shortened 258,missing the rear 2 cylinders.They share the same timing chain,cover,water pump,etc.The 2.5 has a shorter stroke and slightly larger bore than teh 258,but shares a lot of the external components,and some vavletrain parts.It's such a relible 4 banger that it was used in Dodge Dakotas from 1996 thru 2001,instead of Chrysler's 2.5 in the K-Cars.  

I thought the two middle cylinders were dropped to create the 2.5L, and the K-car crap was a 2.2L. Chrysler also had a 2.6L but that was Mitsubishi.  

yeah, the k-cars ran 2.2L as did the rampage and the scaled down chargers of the '80's.  

good stuff, tell us more.  Move to Texas, we could hang out.  

I think you got yer panties in a bunch over nuthin. Much of the modern tech in the Jeep 2.5 made it into the 4.0. No one here said they share the same bolt pattern! They do however share the same modern engine theory of the time. Including the rockers.

And you are wrong. The 2.5L is an AMC motor that was introduced in '84 as a carbed version for use in '84-'86 CJ-7s. In '87 it got a throttle body and finally in '91 it got MPI. So it is in fact older than a 4.0L. Just so ya know, much of the info we ran in our 4.0L history story came from the mouths of the engineers that helped build it.

Sorry about your wasted rant.  

In my response, I stated the question "just because the 2.5l came out first it was the inspiration?" My only comment was that both the 2.5 and the 4.0 should be credited to the old I6 lineage. And the term "Chrysler 2.5l" mentioned in the article is misleading. It is an AMC 2.5l since they weren't Chrysler yet. And another point. The combustion chamber design of the 2.5 was the inspiration for the 4.0 head. Nobody said the 2.5l was newer. The article was not the history of the 4.0 article. That had good info in it. The article by Christian Hazel "Top 10 Jeep Engine Swaps" item 4, is the bone here. It says "1988" and "Chrysler", both wrong.  

Ahhh, I see. That huge rant was only about these two issues???

OK, Ya got me on the '88. We goofed. We are human. Sorry we make errors now and then. Should have read '87.

But, at the time the 2.5L was being built by the new owner, Chrysler...not AMC.

And, the 3.88-inch bore of the 4.0L (among other things) was borrowed from the 2.5L. This means the 4.0L can share rods and pistons from an engine that was designed before it was. So yes the 2.5L was an inspiration.

Also, if we're assigning credit back as far as we can, perhaps we should credit the first manufacturer of the gas engine, or an inline six as well... It's nit-picking. Get over it.  

The reason I said "Chrysler" is mis-leading is because Chrysler actually has a 2.5 motor that is a stroked 2.2 from the K-car. And we know that aint Jeep anything. And it was not meant to be a nit-pick. Just thought it was misleading. Since Chrysler did not aquire AMC until 1987, and the AMC 2.5 came out in 1984, I think "AMC 2.5" is appropiate and not misleading. For general purposes of discussion, and not to nit-pick who actually was on the design team, the AMC 2.5 came out while AMC was the owner, hence "AMC 2.5". It is not my rant, I just thought it was interesting, because it stuck in my mind too.