90 YJ EFI to Carb

[7D8CJ]

Will the intake and exhaust manifolds from a 1990 carburated YJ fit on a late model 4.0 EFI engine? I'm not sure and I would appreciate some insght.

 

[elwood blues]

No. AMC 258 i6 / 4.2l & 4.0L manifolds are not interchangeable.

 

[Cheepjeep85]

i have to disagree, the intake will fit with a 4.0 head, lots of people that do the 4.0 head conversion, use the factory carb intake with a 4.0 header. now i don't believe that the exhaust manifold will work but you wouldn't want to do that anyway, because the 4.0 exhaust manifold/header flows better than a factory cast iron AMC 258 i6 / 4.2l manifold. if i remember right this is the exact same set up rescuediver has, he has a thread detailing the head swap on here somewhere. he used a mc2100, 4.0 head, and 4.0 exhaust manifold, on a AMC 258 i6 / 4.2l AMC 258 i6 / 4.2l . here is his thread, the head swap and details about what you are asking for start at post #60 on this page http://www.jeep-cj.com/forums/f98/im-making-progress-my-project-79-cj-5001/index6.html

 

[Petescj]

i have to disagree, the intake will fit with a 4.0 head, lots of people that do the 4.0 head conversion, use the factory carb intake with a 4.0 header. now i don't believe that the exhaust manifold will work but you wouldn't want to do that anyway, because the 4.0 exhaust manifold/header flows better than a factory cast iron 4.2 manifold. if i remember right this is the exact same set up rescuediver has, he has a thread detailing the head swap on here somewhere. he used a mc2100, 4.0 head, and 4.0 exhaust manifold.

http://www.jeep-cj.com/forums/f2/258-4-0-head-swap-results-8500/?highlight=head+swap+results

 

[elwood blues]

I was under the assumption that they were not interchangeable. Heck, different years of the AMC 258 i6 / 4.2l manifold aren't interchangeable, I was pretty sure they won't bolt up to a 4.0L head, the runners were different.

But, I'm willing to admit it if you can prove me wrong.

 

[Petescj]

I was under the assumption that they were not interchangeable. Heck, different years of the 4.2L manifold aren't interchangeable, I was pretty sure they won't bolt up to a 4.0L head, the runners were different.

But, I'm willing to admit it if you can prove me wrong.

I had to swap carbs because my original cast iron 1978-1979 intake was for a 1 barrel Carter YF carb. The 1980's intake I had to switch to to make the swap work was a two barrel. That shouldn't have affected HP or MPG much during normal operation as long as both were jetted correctly. My old Carter YF was rebuilt and working perfectly. After the head swap I'm barely giving any gas when maintaining 65mph or better on highway up hills, where before the swap I had my foot on the floor and watched my speed drop rapidly!

It's my opinion that anyone with a stock AMC 258 i6 / 4.2l that has the mechanical know how to pull this off should do it asap. They will be thrilled with the results.

PetesCj says: From the above mentioned link

 

[jablonsky]

Let me add more to this for you guys to help. My AMC 258 i6 / 4.2l is shot! # 3 & 4 cylinders only have 50 psi, and the others are under 100. So instead of rebuilding the AMC 258 i6 / 4.2l , I was wanting to pick up a 4.0 to stick in. So with that info, will any year 4.0 work with my intake & carb, and will the bell housing of my 5 speed bolt up to it? Thanks in advance.

 

[yellow85cj]

Here is an 85 intake on a 4.0 head (casting 0630 head). A little messaging on the intake alignment holes to fit the 4.0 head pins, but nothing big.

Here's how I got it to line up.

You will need the 4.0 exhaust manifold.

https://picasaweb.google.com/85YellowCJ7/40HeadSwap#

 

[7D8CJ]

Nice pics and info, Thank you !

 

[Petescj]

I have heard of Yj owners having problems with cracked exhaust manifolds. Can anyone add an upgade for that as well?

Here is an 85 intake on a 4.0 head (casting 0630 head). A little messaging on the intake alignment holes to fit the 4.0 head pins, but nothing big.

Here's how I got it to line up.

You will need the 4.0 exhaust manifold.

https://picasaweb.google.com/85YellowCJ7/40HeadSwap#

 

[yellow85cj]

I think that that is why the manifold in the pic has the "accordion" pieces. Most of the exhaust manifolds I have seen on the yards are solid and do not have them.