I'm trying to figure out the better engine for my yj project. I can choose between an 88 4.2 block with a 4.0 head and MPI, or a standard 4.0 from a 97 XJ. The 4.2 is bored 30 thou over and was rebuilt less than 13k ago. I would swap on either a 93 or 97 HO head to that block after having it cleaned up and a valve job. I would take the injection off the 97 and run that on the 4.2 . I'm leaning towards this idea right now.

I could also just use the 4.0 from the 97 and hopefully not have to worry about any rebuilding costs, besides the fact that it's already bolted up to the trans I need (aw4)

I'm pretty sure the 4.2 engine will make more power, especially down low. It is a bit more screwing around to get that combo to work though. I could also sell what is left from the 4.0 and make some of my $ back, I really doubt anyone will pay much for a 4.2 even though it's mildly built.

A stroker or small block swap is out of the question financially right now, so don't even say they are the only way to go. This will be in a yj with a 60 front, 14bolt rear, 300 tcase, and 39.5 iroks.

Which engine do you think would make more useable power? Or would they actually make about the same power and it will just be more work to run the hybrid 4.2?

4.0l

use the 4.0L. By the time you switch everything over to the 4.2 it will feel just like the 4.0. Also it is slightly more work to use the 4.2.

Beat95YJ, how is it more work to use the 4.2 besides the work that would need to be done with the head to swap that on?

It sounds as though you have a complete running 4.0.

To use your 4.2, you will need to put the EFI and head on it. There are a lot of little incidental things that go into projects like this. What to do for exhaust, accessories, etc.

If the 4.0L is running, toss it in.

i understand that using the 4.0 head is not exactly a drop it on and turn the key thing. i've read quite a few articles about swaping in a 4.0, more on a 4.0 head and mpi swap. i'm just not convinced there is a clear cut best choice. i guess i'm having a problem getting rid of my 4.2 completely because i dumped way too much $ into rebuilding it. Right now I have a complete 88 YJ that is running and a complete 97 XJ that is also running. Neither engine should need anything to be run. I do realize that it will take a bit of work and changes to run the 4.0 parts on the 4.2

right now i like the idea of getting a bit more aggressive cam and adding the FI and 4.0 head to the 4.2 because it should have more power. the only thing people have said about running a 4.0 is that it is more reliable and that it is already ready to bolt in. the rest of my rig won't be ready to run till summer, so i'm not worried about how long it will take to assemble it. I'm not sold on the 4.0 being more reliable than a rebuilt 4.2.

FYI A friend of mine has a Mopar EFI'd 4.0 headed 4.2 in a CJ7. It also has a hesco cam. It has quite a bit more power than my 4.0.

Both!!!
Throw the 4.2 guts into the 4.0 with the 4.0 computer. These engine have different charactoristics. The 4.2 is low end torque where the 4.0 is made for soccer moms in a hurry. This stroker combo could be topped with a HESCO cam giving you the best of both worlds.
Strokers @ Yahoo has all the info.

every place i posted this question i said i can't afford a stroker, yet on every board someone said just build a stroker :flipoff2:

A few people have come back saying just go with the 4.0 for simplicity and ease of getting it running. You've responded you want the 4.2, sounds to me like you have your mind made up and you just want someone to say you should use the 4.2. If you have the time and want the built 4.2, go for it.

every place i posted this question i said i can't afford a stroker, yet on every board someone said just build a stroker :flipoff2:
There are different levels to the strokers, from mild to wild. Wild get really expensive with custom pistons, mild is just the 4.2 crank IIRC.

i'm not 100% sold on the 4.2, that's why I posted here. I have not really heard anything that says one engine or the other is better or worse than the other. It seems like the reply is a 4.0 is easier to deal with or just build a stroker. I'm sure either engine would be fine for what I'm using it for, I was hoping for some people who have built the 4.2 to give their results.

JeepinDoug - I probably could just put in the crank and rods from the 4.2 and get a cheap stroker, but for all the work of tearing into a block with 160k on it I feel like I would want to dore it over and get everything else fresh just so I have a piece of mind knowing that the engine will be solid. The last time I rebuilt an I6 I spent 1300 on it, which is why I say I don't have the $.

If your 4.2 is rebuilt and your comfortable with it just run it with the 4.0 head. If you don't like it you've got something to play with until you decide to swap in a smallblock

Check in on the Strokers@Yahoo group. There is quite a bit of good info there. And like has been said there are very different version.

The simplest is really not much more costly than a straight rebuild and then there are those that can go really wild. Dino's site has a pretty good build up on what he did and it is realitivly simple. Bu tyou nee dto do a little research to fully understand the intricies of the fuel injection and Cam choice.

http://www.jeep4.0performance.4mg.com/

Have fun.

Carl

i think you guys have convinced me to go with the stock 4.0 for now. it's already assembled and it's not gonna hurt anything to keep the 4.2 in the garage. I can save up and build the stroker of my dreams after i get the fuel injection figured out. realistically I don't have time right now to mess around with the 4.2, since I'm swapping frames at the same time I can just pull out the 4.0/aw4/231 and put that in a yj frame and be half done without messing with anything. thanks for talking some sense into me.