4.0 head swap on a .258

[2pwrlftrs4u]

anyone here done this... i have been reading up on it along with the V-8 swap. trying to decide what i wanna do, would like some input on the 4.0 head swap. am i correct in saying that the 4.0 header/exhaust manifold would have to be used but i could use the .258 intake??? i am aware of the 4.0 head needing plugged.

 

[JOOP]

from what I understand you will need a 4.0 head, intake, and exhaust manifold. I dont think you can mix a 258 exhaust with a 4.0 intake or vice versa. They have different bolt pattenrs for the intake/exhaust set-up. It just so happens I have a 4.0 exhaust manifold I could sell you. $50

 

[2pwrlftrs4u]

thanks for the info but i will pass on the manifold..... i will run a header

 

[Not Jobless]

Thanks for the info...I'll pass on the 4.2 and the 4.0L and install a V8.

Too late... I allready did that :flipoff:

Don't waste your time or money on the 4.0L/4.2l/4.7L...what's the point?


You going to polish a POS Dana 30 front for it as well?

 

[Jaydog]

Although I hate to do it, I will agree with Jobless.
Check into the price, I bet you could swap in a Sbc for around the same amount and have a whole lot more torque.

 

[2pwrlftrs4u]

Thanks for the info...I'll pass on the 4.2 and the 4.0L and install a V8.

Too late... I allready did that :flipoff:

Don't waste your time or money on the 4.0L/4.2l/4.7L...what's the point?


You going to polish a POS Dana 30 front for it as well?

sure you can see my D30 anytime you want asshat

 

[Not Jobless]

sure you can see my D30 anytime you want asshat

Sure...I'll come over and we can stand around and down a few while admiring the turds you polished or you can just install a V8 and get rid of that boat anchor.

 

[Not Jobless]

Although I hate to do it, I will agree with Jobless.

That oughta be qotd right there :haha: :haha:

 

[2pwrlftrs4u]

Sure...I'll come over and we can stand around and down a few while admiring the turds you polished or you can just install a V8 and get rid of that boat anchor.

long drive from monroe but get some beer and come on down sat or sun

 

[Not Jobless]

long drive from monroe but get some beer and come on down sat or sun

Let me get this straight...your a Texan and you ain't got a big ass gas sucking jeep with a big block...that's just un-American :flipoff:

 

[2pwrlftrs4u]

Let me get this straight...your a Texan and you ain't got a big ass gas sucking jeep with a big block...that's just un-American :flipoff:

the big block is going in the '52... i do have a V8 on the engine stand right now that may go into the CJ

*you'd be driving to olympia with the beer

 

[NotMatt]

Play nice children. :flipoff:

BTW, I agree with Brad. 4.0's are good motors, and you might be able to frankenstein something together with the 258 block and 4.0 head, but do you really want to deal with possible reliability issues on something like that? Plus from the sounds of it, you want to put a 4.0 head on a 258 and still run the 258 intake manifold, so you won't even get fuel injection out of the deal. The amount of time, money and effort would be better put towards a V8 swap IMO... 'tis what I will do if my 4.0 ever dies.

 

[Totalled]

5.0 Ho. :masturbanana[1]:

 

[Hip]

i studied this for a few weeks before i installed an SEFI 89 5.0 for half the price....

 

[2pwrlftrs4u]

from what I understand you will need a 4.0 head, intake, and exhaust manifold. I dont think you can mix a 258 exhaust with a 4.0 intake or vice versa. They have different bolt pattenrs for the intake/exhaust set-up

i think the exhaust is different but the intake is the same ....or do i need to put down the pipe :corn:

 

[TreeClimber]

Paging Junkyard Jim

If you get serious about doing this, I think JJ has a little more insight.

But I dumped the 4.0 in my YJ and dropped a AMC 401 right in. Mounted to the bellhousing without adapters (as AMC designed the 4.0). All I had to do was buy a set of CJ motor mounts and weld them in. The INSIDE frame dimensions of a YJ are the same width as in the CJ, so they mount easily and nice. Drop in the V8, fab up an exhaust, install a fuel pressure regulator to drop the fuel pressure down, and rewire the engine with the factory AMC harness.

AND I got a 401!

Now, understand, I don't have a EFI motor, but this is a VERY EASY swap, with ooodles of power. And with a Motorcraft 2100 carb, it runs easily at angles, inclines, bouncing, etc. It's really the next best thing to an EFI motor

 

[Totalled]

Yeah... but the AMC V8 supply is kinda drying up... especially the 401 which is high demand.

 

[TheMasterbater]

5.0 Ho. :masturbanana[1]:

Bingo. I :masturbanana[1]: On Brads last weekend. Drooling over the ideas.

 

[junkyard jim]

from what I understand you will need a 4.0 head, intake, and exhaust manifold. I dont think you can mix a 258 exhaust with a 4.0 intake or vice versa. They have different bolt pattenrs for the intake/exhaust set-up. It just so happens I have a 4.0 exhaust manifold I could sell you. $50

It depends what year 4.2L intake. '81 up can be easily modified to fit with the 4/0L exhaust (I've done 2 so far and plan another very soon on my '82 AMC AMX/Spirit along with swapping to EFI later) Earlier intakes were joined to the exhaust and won't fit. I even hooked up the EGR valve and pipe on one with a Renix exhaust so it passed emissions.
The head swap depends on a couple things. If you have a wide block 4.2L (I forget the actual years) you can bolt the head on without filling the water ports on the spark plug side. You can check by test fitting the head gasket and looking for overlap.
The other issue is some have 7/16" head bolts and some have 1/2". You need to put a custom stud in a couple holes or make an alignment dowel fit around one of the headbolt holes if you have the smaller ones.
I think the Renix head is better than the HO for this swap for a couple reasons. The smaller combustion chamber of the HO head, coupled with the improved VE (volumetric efficiency) pumps compression up too much to not run premium gas. Renix head's combustion chamber is still smaller than the 4.2L, but they don't seem to ping as bad.
Most of the HP increase in the HO head over the Renix head is because of the changed camshaft geometry (they use pretty much the same cam as the Renix, but retarded it @10 degrees to cut Nitrous Oxides so they could do away with the EGR valve. This pushed the power band to higher RPMs which also increased HP)

 

[junkyard jim]

Yeah... but the AMC V8 supply is kinda drying up... especially the 401 which is high demand.

After I install the 4.6L stroker in my rig this summer, I have an '86 XJ 2 dr I just got (bought for the 4 cyl motor to get my '86 Comanche rolling again) that I want to pop a 304/727/NP208J combo into. If I can rig the std flywheel setup, I may even go with an AX 15/NP208J combo (since I already have them)
I just need to spend more time working on my stuff and less on the net (like I have the past couple weeks)