I want to run a 258 with a 4.0 head, and i have no current engine. So I want to make sure i pick the engine that is the path of least resistance.

Does the 88-90 YJ 258 block use 1/2 inch head bolts?
AND do they have the 4.0 water ports so that i do NOT have to epoxy the head's water ports?

Other than those 2 things, is there anything else i need to consider about 88-90 YJ block? Sounds so far like the perfect candidate for this swap.

PBB's search function doesn't like to include words such as 258, or 4.0, or 1/2, or YJ, or years. So i figure its been covered and i did try to search...

use things like 258* to get search results, you need 4 characters. no matter what year you pick the water ports will need to be sealed up. they do have the right size head bolts for you though. make sure you get a 91+ HO head.

no matter what year you pick the water ports will need to be sealed up.

Thanks for the search advice...
I found http://www.pirate4x4.com/forum/showthread.php?t=174588

Here Ed A. Stevens writes that the YJ 258 block accepts a 4.0 head without any water port modification. I think Jaffer seems to confirm it. But the entire rest of the internet seems completely devoid of YJ 258H.O. swaps...

Can someone who's done it or seen it confirm or deny this?

If you're building a motor, why not start with a 4.0 block and build a stroker with the 258 crank and rods...?

I'm not building a motor, im hoping to get a bottom end and put a 4.0 head on it. And i want it to be carburated for many reasons. The 4.0 block wont accept a mechanical fuel pump. And i dont want to run high test gas cause its a stroker.

i think a 4.2 with a 4.0 head is a great alternative to a stroker. they can be built way cheaper, and they are much simpler. no need to worry about how your cam will mess with FI, tons of cheap blocks laying around, and lots of low end torque. not to mention the 258 is already a stroker, if i remember right it's a 232 stroked to 258. besides, it's cool to see someone with a different engine. get an hei and a better carb and you will be amazed by the 258.

anyway i would be doing the same thing if i didn't get a killer deal on a complete XJ to supply me with the 4.0/aw4 that I will soon be putting in my yj.

i think a 4.2 with a 4.0 head is a great alternative to a stroker. they can be built way cheaper, and they are much simpler. besides, it's cool to see someone with a different engine. get an hei and a better carb and you will be amazed by the 258.

Exactly... cheap.

Carburation doesnt matter a damn for me in FL, no cold starts, no elevation changes, no steep angles, fuel economy isnt a big consideration, and emissions requirements are dead. What is in consideration is how simple and cheap a carb setup is vs. MPFI.

Im planning to run a MC2100 either on a CJ intake, or a modified 4.0 intake. With a ford TFI ignition. Otherwise its just a 258 with a 4.0 head, maybe a cam down the road. Ought to be plenty of power, and the most headache-free thing i can make...

I can make it a whole lot more headache free if i dont have to epoxy the water ports on the 4.0 head, which i probly wont do right, or will have fail when i overheat the thing! So I'm sorta looking for someone to verify that what Ed A. Stevens said in that post 2 years ago... Cause really hes the only one to have said it. Here it is... Thanks for your help guys.

If you have an 88-90 YJ 258 block you avoid the water jacket problem, because these years of 258 block share the same wide-deck as the 4.0L block casting.

Feel free to post the information regarding the YJ 258 block casting difference: the fact these late 258 blocks share the 4.0L casting molds and the same wide deck surface.

This exercise led us back to the junkyard, where we looked at YJ 258 blocks and identified the different (square sided) deck, identical to the 4.0L block. This is how we found the difference with YJ 258 blocks.

Thanks for the search advice...
I found http://www.pirate4x4.com/forum/showthread.php?t=174588

Here Ed A. Stevens writes that the YJ 258 block accepts a 4.0 head without any water port modification. I think Jaffer seems to confirm it. But the entire rest of the internet seems completely devoid of YJ 258H.O. swaps...

Can someone who's done it or seen it confirm or deny this?

If you have an 88-90 YJ 258 block you avoid the water jacket problem, because these years of 258 block share the same wide-deck as the 4.0L block casting.
87 is a crossover year so an 87 258 should be checked (early or late production YJ, or SJ, can be different blocks).

I have heard at least one other report prior to Ed's posted confirmation that this is true.
It's easy to double check this yourself when the time comes. Any problem matches will become very evident as soon as you test fit them because the 4.0L head on an earlier narrow block will have considerable overhang on the intake side that threatens to expose the head's 12 triangular jackets

Thanks Jaffer, I was just lookin for a 2nd opinion... im gonna head out and look for some parts this week. If the 4.0 head hangs clear off the 258 block in those cases, i should be able to check for myself by measuring the head and blocks mating surfaces.

Thanks again!

Here (http://www.monsterslayer.com/jeep/258CastingIDs.htm) is a chart with I-6 block casting numbers to help you weed out the early, pre-1987 narrow deck versions.

I was thinking about this conversion. A found an article online that has absolutely everything covered. www.off-road.com/jeep/new/40conv.html.