New Here, Recent Cj7 Purchase

Hello all, I've lurked here many times but joined today since I have purchased a `85 CJ7 recently. I've had a little `48 CJ2A for a while now, but needless to say, I have some learning to do on the CJ7. One thing that piques my curiosity is the differences between my 4.2 and the later model 4.0s. I see Edelbrock makes an aluminum cylinder head for the 4.0, I wonder what is involved with swapping one on a 4.2?

 

Welcome from Arvada Colorado

 

Welcome from Cypress Texas~

 

Welcome from Michigan.

 

Welcome from the first state

 

Thank you gents.

 

Welcome from another AMC owner.

 

Why are you interested in swapping the heads? The exhaust and intakes are different I believe. Are you still running the engine control Module and ignition control module?

 

Do us a favor and give some specs.
Tires, gearing, transmission, t case and engine.

A lot of what you do in the future will be dependent on what you have in there now.

 

Welcome.

 

Mostly stock 258; it has the factory electronic ignition and manifolds. A previous owner put a Weber progressive two barrel on it. AMC 20 rear, 2.73s, 30" tires, Tremec 4 speed.

Since my first post, I have learned that the `99 4.0 block is desirable to combine with a 258 crankshaft to build a 280 CI stroker engine. It seems the heads are interchangeable, but you have to be careful to match the correct header/exhaust manifold, intake and valve cover. I think the Edelbrock Performer head uses different year model header and intake manifold.

I'm getting cold feet... starting to sound like a money pit. I'll probably stick with what I have and opt for more modest upgrades.

 

No different than a typical 4.0 head swap, I’d imagine. I just got done putting a 4.2 intake on an early 4.0 head with the matching exhaust manifold.




Had to slightly dimple the two middle runners and a little port matching on the intake. The intake sits a little higher than it did on the 4.2 head also.

 

Nice! Thanks for the pics.

 

There are water ports that are different between the 4.2 and the 4.0. On my 4.2 when it needed to be rebuilt. I went to .60 over pistons and a small RV cam with a motorcraft 2100 carb. I deleted all of the computers and installed a HEI distributor. I have more torque. I also did the nuter bypass for HEI which you will remove a box load of useless cable and parts. But if you live in a state that does emissions I would see if your year vehicle is exempt from testing.

 

I think you are starting at the wrong end of your woe's.

First to be addressed would be the horrendous gearing. In your long term planning, pick the tire size, transmission (swap, if any), and wheeling terrain/driving application you see yourself in and choose the gearing to fit that criteria. Look for cruising RPM's as well as any added needs in the first gear area. You will be amazed at the added power from a set of stock 3.73's will give you. With anything over stock tires, the MPG's will go up too.....

Webber 32/36? The smaller 2bbl progressive is considered too small for the 258 and a swap to the 38/38 or a 2100 Motorcraft will garner large improvements in power without any major surgery.

 

Agree with the need for gears, I was thinking 3:54 ratio.

The Weber is a new thing to me so I've been researching it extensively. Info is somewhat inconsistent, but the website suggests it was designed for no more than 2500 cc four bangers. The 38/38 is supposed to be better suited to six cylinders but for the money, not sure it's really big enough either. The one I have sure does work smoothly, but you can feel power fall off as rpm goes up.

Clifford sells a manifold and carb setup with twin Webers, I like it mucho but its a bit spendy when I have other areas that need addressing first.

I like the Motocraft 2100 suggestion, $90. on Amazon.

 

Update: Interesting IF the internet is correct, the Motocraft 2100 flows 300 CFM with a venturi size that is smaller than both Webers. So maybe the 38/38 is good for 390 CFM. BTW the 32/36 is recommended by Weber Redline for the 258 Jeep when stock. Internet says it only flows 240 CFM.

 

Nothing but horror stories about the 32/36 being inadequate for the I6.

The 38/38 properly tuned will run rings around the 32/36. A genuine Motorcraft 2100 with 1.08 venturi's is a proven upgrade for a fraction of the price of a Weber 38/38.

Or you can splurge and spring for a 4BBL manifold and a Holley 390 or the like.

 

I have had zero issues with performance with my 4.2 with the MC 2100. Ford used it for years on 289’s and 302’s in the F100. And a good part is you can get them at your local O’Reilly’s

you will have to pick up an adapter to convert to the Jeep intake. I’ll take a photo tomorrow and post.