I was driven, like many of you, into my engine build-up when my old engine died (with the help of a dead water pump I managed to crack the top end of my 20-year-old 4.2). So with my (at the time) daily driver out of commission, I needed a fast, cost-effective solution to my problem. My options were pretty slim for the budget I had, but I decided that, no matter what, I could not justify keeping a totally stock 4.2...So I opted to go ahead and install a 4.0 head to my existing 4.2 block.
The installation of this swap is as simple as pulling and re-installing a stock 4.2 head. All the work is in the preparation and modifying existing components to accommodate the new head.
Here is a list of what you need:
- 4.0 Head (post-1994 preferred)
- 4.0 Valve Cover
- 4.0 Head Gasket
- 4.0 Header or Exhaust Manifold
- 4.0 Intake (not necessary, but STRONGLY RECOMENDED)
- Head Bolts (don't be cheap, buy new head bolts!)
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* Special Note: This is a performance modification, and retaining stock parts may hinder your performance. I recommend upgrading your intake, exhaust, and carb due to the higher flow and output of the new head. Again, this isn't necessary, but if you don't do it, it negates the purpose of the project, right?
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I started with a HO 4.0 head from Clifford Performance. To make the 4.0 head function properly with the 4.2 block, it is necessary that you block all 12 of the water jackets on the passenger side of the head. Although many write-ups suggest that you can (or even should) use a high temp epoxy to seal these jackets, I strongly urge against it. I have tried this and ended up having to pull the head multiple times. In the end, the jackets usually blow out if sealed with epoxy, so do it right the fist time - pay a machinist the 200 bucks or so to seal these water jackets with a copper weld and then have them perform a valve job and resurface the head. This is the only right way to do this right...don't try to get around it cheaply; it does not work (trust me on this). With the head purchased and prepped, I was ready to remove the old head and get the project up and running.
Removing the existing head is easy work for someone who is mechanically inclined. All the removal information can be found in any good tech manual, and requires no special tools. If you are retaining some stock parts, make sure to keep them tagged and / or marked to make re-installation more bearable. You will be re-using your stock pushrods and rocker arm assemblies, so set them aside and try to keep them in order. Since I retained very little of my stock parts, I ended up just tearing most of it out in a fit of glee.
Installation of the new head is basically working backward from what you just did. At this point I decided to upgrade a few things. I opted to go with a new Clifford intake to accept my new Edelbrock 500 cfm 4-barrel (yes, you will need that much air/fuel flow - I tried three carbs before I determined that. Don't waste your money like me, do it right the first time). Along with the carb and intake, I bought a Clifford Stage 2 header and a nice new valve cover. Again, installing the head is straightforward, the only "special tool" you will need is a torque wrench.
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*Note: You can use EFI systems designed for a 4.0 with the new head! These are available from Howell, Mopar, and if you really want to go all out, Clifford makes their own HP system.
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Here are a few things that you may run into that will cause more than a little grief here and there that most write-ups don't tell you about:
- If you have power steering, you WILL need to modify your bracketry to make room for the 4.0 headers. By this I mean "go grab your angle grinder and have some fun". Make it fit - all that bracketry isn't necessary after the new head is installed (this will be self evident when you get to that point).
- Another thing that goes unsaid in other articles is the issue of smog equipment. Simply put, I didn't use any. I don't know how you can retain all the smog stuff, especially while doing away with your Carter carb. You can get most of the parts you need from Clifford with tap holes for accessories, but again, unless you have to retain that stuff - just throw it out.
- Your stock exhaust system may not accept the new header - mine didn't. So, being the rebel that I am, I decide simply to run straight headers in California for a while...needless to say the cops liked that. Later I had a new system made for me.
In the end, this swap is a no-brainier. Initially I had some difficulty getting it all worked out, but if you heed my words and do it all right the first time, it should only take you an afternoon to do. Cost range can run from dirt cheap (junk yard head, etc.) to very expensive...or anywhere in between. Regardless, I think you will be as happy with the results as I was.
The head alone will gain you 40 HP and 10% mileage increase, and with the option of upgrading the rest of your intake and exhaust systems, you can easily gain 100 HP for a reasonable Horse-to-Dollar ratio.
In the end, the pay off was incredible. I ended up with a CJ that had around 215 HP (that was then - I have more now) and still got 14 MPG driving with 38's; all for a lot less than the price of a V8 swap and definitely for a lot less work. For more information, please feel free to write me and or call up Clifford performance - I can vouch for how helpful and knowledgeable are - they don't call 'em the "Inline Specialists" for nothing!
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