258 vs 4.0L

[defibvt]

I live in AZ. A/C is a must and power steering is nice with 35's. Which motor do I choose? I already have AMC 232 i6 that is bored over .40 and has RV cam. The issue is finding brackets for a/c and power steering are like trying to find hen's teeth for a AMC 232 i6


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[Peanut Butter]

Gearing is everything when you have 35's. That being said, I have a Jeep Cherokee too. It has a 4L with AC and power steering. I use it for an emergency vehicle. It will get up and go and run all day. I only have 245's on it, so anything bigger would really drag it down and hurt mileage without the right gears. If I could buy a complete 4L with all the electrical, I would get it for my CJ. Hope that helps some.

 

[Scout1067]

Somebody correct me if I am wrong but it is my understanding that the difference between the AMC 258 i6 / 4.2l and 4.0l is the head and valve cover from a pure parts perspective; the block is the same?

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[caveman]

Somebody correct me if I am wrong but it is my understanding that the difference between the AMC 258 i6 / 4.2l and 4.0l is the head and valve cover from a pure parts perspective; the block is the same?

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Pretty much so. The 4.0 has a shorter stroke and larger bore. At some point they blocked off the fuel pump boss because they put the fuel pump in the tank. Also, The head bolts changed size.

 

[defibvt]

So, my concern is that installing the AMC 258 i6 / 4.2l is pretty straight forward swap from my AMC 232 i6 . Installing the 4.0 is whole different animal that is out of my shallow depth of knowledge. The AMC 258 i6 / 4.2l would be easier, however the benefits of the 4.0 are numerous. Do I make leap or stick to the easier option. My resources i.e. friends that know things near me are very Limited .

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[coldair]

The bocks are really close but not the same. You can interchange almost all the parts from a AMC 258 i6 / 4.2l to the 4.0 block. I used my power steering, AC bracket, alternator, water pump, front timing cover on the 4.0 block that I have in My jeep right now. Ive had both in my jeep.
Now if you are looking for a 4.0 go with the earlier block because the later block wont just bolt in. When I did mine I had to tap one of the motor mount bolt holes one size bigger.

 

[defibvt]

The bocks are really close but not the same. You can interchange almost all the parts from a AMC 258 i6 / 4.2l to the 4.0 block. I used my power steering, AC bracket, alternator, water pump, front timing cover on the 4.0 block that I have in My jeep right now. Ive had both in my jeep.
Now if you are looking for a 4.0 go with the earlier block because the later block wont just bolt in. When I did mine I had to tap one of the motor mount bolt holes one size bigger.

What years would you consider earlier?

 

[coldair]

Obd1 so 1991-1995 as 1991 is the first year of the ho 4.0 I believe.

 

[berserk71]

So far, I really like my Clifford performance built AMC 258 i6 / 4.2l . Lot's of torque and better mileage about 20mpg with room for improvement. The AMC 258 i6 / 4.2l could be thought of as factory stroker compared to the 4.0. The AMC 258 i6 / 4.2l is known for low end torque where the 4.0 is more of an emissions compromise made to produce it's power at higher RPM. Low RPM torque, IMO, is more controllable off road, offers easier drivabilty on road and is capable of better mileage, if set up properly, in my experience. The AMC 258 i6 / 4.2l head has a longer narrower intake passages which is generally considered desirable for low rpm torque but restricts air flow at high RPM. The 4.0 is just the opposite. IMO, the AMC 258 i6 / 4.2l is a better general on or off road engine but not in it's stock configuration. Intake/exhaust manifolds, distributors, carbs and ignition where not that great from the factory. The AMC 258 i6 / 4.2l heads also have little tiny intake and exhaust valves which the Clifford kit will fix.

 

[defibvt]

I have a T-18 ,Transmission with granny gear and Dana 300 with Lomax 4:1 gear ratio. I will be ok.

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