258 or 360?

[BlackOmega]

Depends on what you're going to use it for.

While the 360 is an ok motor and all, to make any decent power out of it, you'll need to cam it, that, in and of itself, will make you lose your low end torque.
If you're not going to be doing some hardcore bogging, or anything else that requires tons of HP, then, I believe, the AMC 258 i6 / 4.2l would be a better option.

Great low end, tree stump pulling torque.

 

[Petescj]

The more I think about this the more the AMC 258 i6 / 4.2l makes sense for me. The kind of wheeling I enjoy lends itself well to the low end grunt and idle of the AMC 258 i6 / 4.2l . Hopefully the 4.0 head upgrade will make towing my small "Jeep" trailer a little easier. I "think" I'll need to gear the Limited around 4.56 with the 35s. Still planning.

 

[jdarg]

A fuel injected AMC 258 i6 / 4.2l should make more HP than a stock, late 70's 2bbl 360 if that helps.

That said, I'd run the 360 and GM TBI it.

 

[ThisGuyUKnow]

Do you already have the AMC 258 i6 / 4.2l ? If so then go that route with FI. If you dont have either and have to buy an engine get a 4.0. Or go crazy with it and take the crank from a AMC 258 i6 / 4.2l and have the machine shop build you a 4.6 stroker.

 

[Petescj]

Do you already have the AMC 258 i6 / 4.2l ? If so then go that route with FI. If you dont have either and have to buy an engine get a 4.0. Or go crazy with it and take the crank from a AMC 258 i6 / 4.2l and have the machine shop build you a 4.6 stroker.

Yeah I have a AMC 258 i6 / 4.2l that needs a rebuild. Im hoping the 4.0 head swap will be as good as others have said. Im not even thinking carb on this one.

 

[deadfeat]

Yeah I have a AMC 258 i6 / 4.2l that needs a rebuild. Im hoping the 4.0 head swap will be as good as others have said. Im not even thinking carb on this one.

A 40 l from a 91 to 95 xj is a very easy swap. Get the entire donor and part it out to recoup the cost. Then you get the computer harness and all.

Sent from my Galaxy S3 with Taptalk 2

 

[cj7inthetwigs]

I am so torn between the AMC 258 i6 / 4.2l and 360 I dont really know what to do. The Limited obviously came with a AMC 258 i6 / 4.2l but it would need rebuilt anyway. The last few Cjs Ive had convinced me that the AMC 258 i6 / 4.2l is a great little engine. Im really happy with the 16/17 mpgs Ive been getting out of the Laredo as well. Im just not sure its what I want to put in "My Jeep".

Since Im already going to be running a SM465 behind either motor Im not worried about any breakage. I'll be upgrading my stock axles as well. If youve read this far you noticed there are only 2 choices. I dont want a Chevy 350 , Ford blah blah blah. These are the only 2 engine choices for my Cj.

I just dont know if the 4.0 head mod will be enough to make me not crave the V-8. I loved the 360 in my CJ5 , just not coupled to the T-150 and Dana 20 . The 12/13 mpgs wasnt very attractive but Im not into these Cjs for gas mileage. Either one can be set up for fuel injection so thats a wash.

Commence argument

Yep, its a hidden message!

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[johnnyreb]

you need the rods out of the AMC 258 i6 / 4.2l too. Punch the 4.0 .030 to make the 4.6
I'd look into a high compression piston for the AMC 258 i6 / 4.2l with 4.0 head. I'm planning to do the head swap onto a stock AMC 258 i6 / 4.2l and hope to regear from the 2.72's

 

[jdarg]

Please nobody take this personally if you run a 4.6L.....

Don't HE pistons to make a stroker 4.6L cost ~ 600 bucks, or like $1000 if you go cast? As much as I love the i6 this seems beyond the point of reasonable returns for the investment. Thats more money than a high quality 4.0L engine kit. I understand the thrill of the challenge but in the end its...just a cast iron 4.6L.

Never mind that hardly anybody (like 1-2 companies in the world) can re-tune a Jeep ECM for it properly either. Adjustable MAP sensors and slightly bigger injectors are a kludge so people don't blow up their motors, but far from optimal tune under all engine loads and speeds. If I ever did it, I certainly wouldn't use a Chrysler/Jeep ECM to run it. It seems silly to go that far with the mechanicals and then totally compromise the engine management.

In a CJ where you don't want a v8 I would just do the whole MPFI 4.0L swap, w/ the Hesco crank trigger for CKP and a 91 YJ analog/digital VSS sensor on speedo cable, and be done with it. Wouldn't even do a head swap onto a AMC 258 i6 / 4.2l . 4.0L are cheap and your local yard has 5-10 sitting there right now. If the AMC 258 i6 / 4.2l runs good, sell it to offset the 4.0L.

 

[deadfeat]

...

In a CJ where you don't want a v8 I would just do the whole MPFI 4.0L swap, w/ the Hesco crank trigger for CKP and a 91 YJ analog/digital VSS sensor on speedo cable, and be done with it. Wouldn't even do a head swap onto a AMC 258 i6 / 4.2l . 4.0L are cheap and your local yard has 5-10 sitting there right now. If the AMC 258 i6 / 4.2l runs good, sell it to offset the 4.0L.

Better yet. Buy a low mileage 91-96 XJ running. Odb1 swap is easy. I swapped in the aw4. No hesco needed. Thick Dana 300 clocking ring and a vss speed sensor. When your done, part out the cj. I ended up, $300 in the black after selling all my AMC 258 i6 / 4.2l parts and the xj parts.


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[Hedgehog]

Why would anybody in their right mind "part out a CJ" when there's a perfectly good XJ to crush?

 

[deadfeat]

Why would anybody in their right mind "part out a CJ" when there's a perfectly good XJ to crush?

Lol. Correction part out xj

Sent from my Galaxy S3 with Taptalk 2

 

[ThisGuyUKnow]

Please nobody take this personally if you run a 4.6L.....

Don't HE pistons to make a stroker 4.6L cost ~ 600 bucks, or like $1000 if you go cast? As much as I love the i6 this seems beyond the point of reasonable returns for the investment. Thats more money than a high quality 4.0L engine kit. I understand the thrill of the challenge but in the end its...just a cast iron 4.6L.

Never mind that hardly anybody (like 1-2 companies in the world) can re-tune a Jeep ECM for it properly either. Adjustable MAP sensors and slightly bigger injectors are a kludge so people don't blow up their motors, but far from optimal tune under all engine loads and speeds. If I ever did it, I certainly wouldn't use a Chrysler/Jeep ECM to run it. It seems silly to go that far with the mechanicals and then totally compromise the engine management.

In a CJ where you don't want a v8 I would just do the whole MPFI 4.0L swap, w/ the Hesco crank trigger for CKP and a 91 YJ analog/digital VSS sensor on speedo cable, and be done with it. Wouldn't even do a head swap onto a AMC 258 i6 / 4.2l . 4.0L are cheap and your local yard has 5-10 sitting there right now. If the AMC 258 i6 / 4.2l runs good, sell it to offset the 4.0L.

I was more kidding about the stroker. Honestly if I ever went with one I'd just get a crate stroker from quadratec over having a shop build me.

Honestly a healthy stock AMC 258 i6 / 4.2l bottom with 4.0 head and FI is a good ride. I know because I used to have one (And I have regretted selling it ever since i did it)

 

[Petescj]

Honestly a healthy stock AMC 258 i6 / 4.2l bottom with 4.0 head and FI is a good ride. I know because I used to have one (And I have regretted selling it ever since i did it)

Im 75% sure this is what Im going to do. That jumps to 95% if your going to do my wiring harness.

 

[ThisGuyUKnow]

Im 75% sure this is what Im going to do. That jumps to 95% if your going to do my wiring harness.

I may hit up the u pull this weekend and molest a xj and put something together as a trial run to put one together to see what kind of commitment id be getting into.

 

[Petescj]

I may hit up the u pull this weekend and molest a xj and put something together as a trial run to put one together to see what kind of commitment id be getting into.

I have to figure out everything I need from the correct years and all before I plung into that. It definately wont be till after Christmas. You know better than I what is needed. I pretty much need a carbon copy of what yours was considering its going into almost the exact same Cj. We're gonna have to get together and talk sometime.

 

[ThisGuyUKnow]

I have to figure out everything I need from the correct years and all before I plung into that. It definately wont be till after Christmas. You know better than I what is needed. I pretty much need a carbon copy of what yours was considering its going into almost the exact same Cj. We're gonna have to get together and talk sometime.

Do you want to try and convert it to the serp as well? or are you just going to stick with vbelt? Will you be going with an ax15or nv3550 or will you stick with a AMC 258 i6 / 4.2l tranny?

 

[Petescj]

Do you want to try and convert it to the serp as well? or are you just going to stick with vbelt? Will you be going with an ax15or nv3550 or will you stick with a AMC 258 i6 / 4.2l tranny?

V belt most likely and Im using a SM465.

 

[ThisGuyUKnow]

V belt most likely and Im using a SM465.

then should be ready. must expensive individual part will be the cps relocation dampner.