4.0 Head Conversion

I know this has been talked about before, but I just have a question or two. I have a 75 258 that I am going to put a 4.0 head on, a 7120. I know I will have to use the 4.0 exhaust manifold, but will my 258 intake with carb work on the 4.0 head, or how will I have to modify it. Gathering parts to do this as a weekend project. And on a very strict budget...Thanks in advance for your help.

 

You want to use your 1972 1V cast iron intake? My sources say the 81-on aluminum intake certainly will, but I don't know about the earlier iron intakes. The bolt pattern is right, but I don't know if the thickness where the washers bridge the intake and exhaust is right. Also, I don't know if the extra iron around the carb heater (4 bolt flange) will clear the later exhaust manifold.

What kind of carburetor will you use?

 

Timgr...I guess I asked the wrong question....I do have the original iron 72 intake and carb, but what I was looking for was what newer intake (alum.) would work that would use a 2bbl carb. I would use a 2100 Motorcraft. I think you answered part of the question, 81 and newer, but how new can I go without alot of mods?

Thank You

 

Is there anything specific that needs to be done to line up the ports on a later intake and the 4.0 head?

 

AFAIK all the aluminum manifolds for the 258 are basically the same from 1981 on. Tim Weaver's article (no longer on the net) says you can use your old 258 intake manifold. Nothing needs to be done to make it line up other than to position it correctly and to use the 4.0L washers, again AFAIK - I have not done this swap. As I understand it, the 4.0L HO intake ports are the same pattern as on the 258, but they are higher up on the head with the port pointing more down to the valve than on the 258 head. This means that there is more vertical distance between the intake and exhaust manifolds.

 

What's the best stuff for blocking off the unused cooling passages in the 4.0 head?

 

MacGuyver would use bubble gum and if that didn't work, some duct tape.R)

 

Great. Just what I needed to know

 

The three methods I've ehard of are
1) weld,
2) machine a cylindrical pocket over them and seal with a freeze plug, and
3) fill the holes with soluble packing peanuts, and fill over with JB Weld. File/sand smooth.

 

As a note the locating pins for the intake on a fuel injected head are in a different location than on the earlier carburetor heads. Least ways this is true with the 94 4.0 mpi engine that I have in the shop and the 258 in the Jeep, when the mpi manifold is on the 258 locating pins the ports do not line up. The holes in the intake can be welded and re-drilled if needed to align the ports. Look at the intake gaskets between the different heads you should see the slight difference.

 

Good to know. Being that I have a sticking lifter, I may do a 4.0 head conversion since I will need to pull my 258 head to change the lifter. Don't know why AMC didn't put in lifter access covers on the side of the block like Chevy.

 

STILL on the net: http://www.monsterslayer.com/pages/jeep/40Head/40Head.htm

I did this conversion and absolutely LOVE it. Some of you have already read my basic write up : http://earlycj5.com/forums/showthread.php?t=53136 . I use my original intake and carb..but that's not gonna help you Colorado since yours is a pre-1981. I did my HEI Upgrade at the same time, so I noticed a HUGE difference.

I'm getting 23mpg! I wouldn't believe it if I didn't have 20 witnesses from my 4x4 group watch me top off my tank with 5 gallons after driving over 100 miles!

Anyways, I too filled my water jackets with peanuts and JB Weld. I was worried about this being not efficient enough, but there's really no pressure or anything to worry about with the water jackets.

Anyways.....this is my Daily Driver "budget rig". 8,000 miles later and I have had NO problems!!! (knocking on wood).


My 2 cents!R)