Jeep 258 to 4.0 conversion

[72jeeperjoe]

I am sure this has been covered, just looking for information. Is there and modifications needed to put the 4.0 intake onto the 258 head? I am not doing a 4.0 head conversion, I just rebuilt my head. I am converting to fuel injection with the harness etc and do not plan on running serpentine yet. Thanks everyone!

[babywag]

You'll find way more information on other jeep forums vs. here.
It's well documented there, but very little info on this forum.
A google search provided a wealth of reading on the subject.
My nephew want to do the same @ some point with his 258.
Although it may get GM TBI first, and MPFI later?
Since his engine is basically all new, a 4.0 head swap isn't on the list.

[72jeeperjoe]

Thanks for the info, I will do some searching. I don't plan on the head swap either but I will be running mpfi.

[72jeeperjoe]

If anyone else needs info I found a good right up at jeepers forum, it was the first result in the google search. From what I understand the only real modification needed to install the intake is new holes for the dowel pins in the head.

[yossarian19]

I understand that you just sunk money into the 258 head but I think you need to ask yourself "why aren't I building a stroker yet?"

[ThisGuyUKnow]

I understand that you just sunk money into the 258 head but I think you need to ask yourself "why aren't I building a stroker yet?"

Well not necessarily that but you really should consider swapping to the head maybe b you can sell your rebuilt 258 head. Your gonna see alot better performance with the 242 head and injection together. Part of what makes the 4.0 more powerful is that redesigned head

[Cecil14]

I think you're going to have a hard time putting the 4.0L MPFI intake on a 258 head without the recesses in the intake ports for the injectors. The 258 intake is just the square intake ports (been a while, going by memory here), while the 4.0L has little notched spots for the injectors.

Here's a comparison:

http://www.geocities.ws/cecil_odo/stroker/47stroker/47intake1.jpg

The top is a Renix (if I remember right, been like 15 years) head, middle is a 4.0L (again Renix I think) intake, followed by a cast iron 258 intake on the bottom.

It's possible to do, and I'd definitely say throw it on and see how things look, but I think you're going to have problems with the injectors.

FWIW, you're REALLY limiting yourself by sticking with the 258 head, rebuilt or not. The 4.0L honestly is leaps and bounds better.


aa

[72jeeperjoe]

My plan now is to buy a complete 4.0 and swap everything over at once. I currently have a 94 4.0 with the fabled 7120 head. I wont be completing the swap until February due to my time frame. I will be swapping over the head and intake with fi etc and keeping the block to build into a 4.6 stroker down the road.

[J20 project]

I found an extremely nice 81/82 ish J10 w/ matching shortbed topper kinda reasonable w/ 258 torn apart. I think it would be a perfect 93 and newer OBD2 4.0 swap would be awesome.

J20

[72jeeperjoe]

Yeah that would be a sweet swap. I love the 4.0?s, I like the 258?s but for everyday driving you can?t beat the 4.0

[Cecil14]

I found an extremely nice 81/82 ish J10 w/ matching shortbed topper kinda reasonable w/ 258 torn apart. I think it would be a perfect 93 and newer OBD2 4.0 swap would be awesome.

J20

Just curious, what do you see as the benefit from the OBD2 setup? I've never really looked into it, as I had the OBDI stuff on-hand. Obviously the potential for OBDII scan tools would be pretty awesome, but is there something else? I've never found the OBDI ECU to be limiting to anything I've done, and if I really started getting radical, I'd likely want to go MegaSquirt anyway. I don't think the OBDII ECU would save me anything there.


aa

[yossarian19]

OBD2 is easier to read codes from and the codes themselves are more sophisticated / easier to diagnose. I don't think the sensor package changed any, at least until 2000 when they went coil on plug (no distributor) so aside from scan tools & codes, I don't know what OBD2 brings you. For me, those two are enough reason to go 96+ engine management (or megasquirt)