want more power not getting it with tired AMC 258

[1990wrangler]

I want to get more power and was looking for options for my 90 wrangler it has a AMC 258, hei distributor, howell tbi kit, this doesnt sound like much but it took me two years to finish it to where it is now but i am not happy with the results. i want more power but di have alot of money wrapped up in the jeep already and eveyone keeps saying its a money pit. i enjoy working on it and have had alot of fun doing it. I would like to build a stroker but what parts can i use from 258 this site mostly talks about building up 4.0 but i dont have one i have a 258 which has all the parts for a stroker. but i would like to keep carburated or in my case fuel injected tbi bc i dont want to loose the money i spent on that (1200) not worth it at all. question is what can be used and where should i start. will the stroker bolt to my bellhousing and tranny which is ax-15, and np231 transfer. changing transmission is not an option either just had that fully rebuilt(1800) about 1000 miles ago. thanks for your input hope you can help

[92tank]

Well you already have the hardestd to find parts inside that 258. Know all you need is a 4.0 block and head as they flow much better than the one you have, and your intake should fit just might need to massage it a little. You can find a good 4.0 in the junk yard or on the internet for under 300, and if you can find one that someones pulled cause it burns oil that's fine too as it will all be gone through. As for the rest of the parts you need there are some recipes on this site that list the parts you need. If its built right a stroker will def wake it up.

[amcinstaller]

agreed. alot of what you have now will work. just find the 4.0 and even do a cheaper 4.5 or 4.6 and you should be laughing. i might have missed it somewhere but what cam do you have, stock 258? ooohhhhh, also will have to figure accessories mounting. im in the same boat cause my car had a 258 and the alternator bracket doesnt fit. if you can weld i bet you could build one tho.

[92tank]

The renix ran a delco alternator, I noticed that the other day at the junk yard so that might be an option for you guys wanting to keep with the v belts. And there cheaper to rebuild than the ones that the HOs run

[1990wrangler]

are all the 4.0 motors in the 90's high output bc only most of them actually say it on the look out for one if anone has one

[SilverXJ]

I think 90 or 91 was the first year for the HO engine. All engines after that are HO as well.

[Muad'Dib]

91+ HO 90MY was still RENIX.

[amcinstaller]

91 sounds right to me too.

[1990wrangler]

another question I told asked my boss if he knows anyone selling motors and he said yeah but isnt yours a 90 and i said yeah and he said that it will not mount without a kit, he said that the frame drops in the front differently and i would have to buy extra stuff to mount the motor in the factory 90 mounts any information would be helpfull still a virgin havent tried to stroke it yet thanks

[amcinstaller]

i dont see why it would be a problem?? i could be wrong but im sure its been done before, 4.0s and 258s are the same outer dimensions. but you do need to use your oil pan, maybe thats what he meant?

[jeepman]

A 4.0L will bolt right in place of the 4.2L without any modification in a YJ and that includes the oil pan.
You will have to change the pilot bearing to mate the engine and trans if you have a manual trans.
You will also require an electric fuel pump for a 4.0L because the 4.2L has a mechanical pump where the 4.0L does not.


I have done dozens of 4.0L swaps.