258 options

[CJ RIGGS]

I've decided to go back with the original AMC 258 i6 / 4.2l . I plan on having it rebuilt if the block is serviceable. My questions revolve around increasing horsepower.
•What head options do I have?
•same with intake (mine is cast alum.)
•I would eventually like to adapt EFI to it. And electronic ignition.

I like the idea of keeping the engine original but would like more horsepower.
My endgame is to have the original CJ look, including original color and engine. Modernize the mechanics, lights and gauges. And kick the tires up a notch to 31" M/Ts.

 

[mtnwhlr]

The 4.0 head is a good upgrade. But if you want power swap in a 4.0 stroker.

 

[Torxhead]

I am a big fan of the fuel injection for the CJ. The Team Rush ignition upgrade is great also, but if the efi you are planning on has a computer controlled ignition then there is no sense in it. Although it is a very inexpensive upgrade. A good gear ratio/tire diameter is critical also.

 

[gert]

Edelbrock head, 2bbl intake with GM TBI, higher ratio roller rockers, higher compression and a good header

https://www.quadratec.com/products/...6gbzh1FUOhKedevEpUmsH7UzwBp--qvBoCw9QQAvD_BwE


Sent from my iPhone using Tapatalk

 

[hole]

4.0 head and Mopar MPI and you will be a happy camper

 

[RattleTrap]

I struggled with the same questions - I wanted to keep it original as possible with some additions to make it more dependable as a "fair weather" daily driver and a good off road toy. In the end I was more interested in low torque than HP and AMC 258 i6 / 4.2l was my platform of choice.

The original engine had 200,000+ very hard miles on it when I bought the CJ. So I had it bored 40 over due to wear, completely rebuilt, cleaned up the head, installed a Howard cam, and the Mopar (HESCO) MFI. The Mopar MFI is a speed density (vs. MAF) fuel injection system based on state of the art 1980's technology and did not play well with the increase overlap and lift of the cam. Luckily for me this problem is not unique to jeeps and there are a lot options to deal with the problem, but it is one more technology and investment. Ultimately I had to add a Piggy Back tuner and a wide band O2 sensor with gauge to fine tune the Mopar (HESCO) MFI. But I am happy with the low end torque as well as the power curve.

I took me about 2 months of learning and playing with tuner (Split Second PSC1-003) to come up with a set of Air Fuel tables (MAP voltage off-sets) that I like and gives me a torquey little jeep that is fun to drive on the street or trail.

Another challenge for me was the 7/16" head bolts used in the '84 AMC 258 i6 / 4.2l 's. I was forced to replace the factor head bolts with 1/2" head bolts. One or two of the 7/16" head bolts would pull out of the block about every 900 miles. All in all I pulled 4 head bolts from the block. After the second time I chose to have it upgraded to 1/2" head bolts. This meant drilling head & block to accept the 1/2" bolts.

Not counting he MFI system I have about $2,500 in the engine.

If I had it to do all over again I think I would go with a stock cam & the Mopar MFI. That is of course, unless you really like the thrill of tuning.

 

[CJ RIGGS]

I appreciate all of the advice. Thank you.

Another question i have. The engine has 77,000 original miles on it. Is there any benefit to rebuilding the original engine vs just swapping mine in for another just like it?

 

[Torxhead]

I would vote for the original rebuild. The 4.0 crank and head would really add power.

 

[hole]

X2 on the original

 

[CJ RIGGS]

I looks like I'll have to move on to plan B. My AMC 258 i6 / 4.2l had multiple cracks in it.