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I have a 96 xj with a 4.0l obdII... In an emissions state. Can I use a 4.2 block and my 4.0 top end and still keep all my sensors and running gear the same? Looking at the 4.2 cause I have access to one real cheap and this is my DD. I have seen the 4.0 top ends on 4.2 short blocks before but haven't seen anywhere about the obd2 end of things
Its your first post so I will go easy on you before anyone else decides to give you real bad time.
The 4.0 motor has a bigger bore (larger pistons) that the 4.2. The 4.2 has a longer throw crank which is why it has more displacement despite the smaller pistons. When you put the 4.2 crank (long throw) into the 4.0 block (big bore) you are "stroking" the 4.0 (which is why its called a stroker). The end result is anywhere from 4.5 to 4.7 liters depending on the size of the overbore.
Using the 4.2 block would be pointless. Putting the 4.2 crank back in gives you 4.2 liters. Putting the 4.0 crank in would give you something like 3.7 liters.
The 4.0 head on the 4.2 motor is a great swap. Much better head flow and more power.
The answer to your question is YES but its going to be a real pain.
Your going to get into all sorts of weirdness with the brackets for your PS, AC, Alternator, CPS, not to mention pulleys and belts if you build a tiny little destroked AMC 258. Just keep the 4.0 and rebuild it if its shot or get one from the junk yard out of a crashed vehicle and swap it in.
The cyl wall thickness will likely be way too thin if you expect to get any stroker-like displacement out of a 4.2 block. A 4.0 block is what, 50 bucks? maybe 100?
You may or may not be able to punch the block out that much. I don't think you'll be able to gain enough, a 4.2 has a 3.75" bore and a 4.0 has a 3.88" bore. 130 thou is a LOT to bore out. Most people seem to say you can bore out to about 60 thou over.
And up here in the rust belt engines are cheap. If you are going to do machine work/bore it out etc anyways, you can use damn near any 4.0 that hasn't thrown a rod or cracked a water jacket, you probably can get one with a spun bearing or something for free.
Binghamton area will have sales at Pick a Part on engines for $100. They generally will have a half a dozen HO year XJs.
What's wrong with your existing 4.0 block? You can put the 4.2 crank in the 4.0 block - that's the way for the stroker. Obviously it's not that simple (piston, possible rod swap), but that gets you to the 4.5-4.7L size, as Ken mentioned. Using the complete 4.2L bottom end with the 4.0 heads and manifold is not likely to be worth the effort for the displacement and stroke improvement.
Trying to keep this 4.0 running as until the other is ready to be dropped in... This my daily driver. My plan once I have the stroker built and ready to swap it over the weekend. I can barrow my girls car if it takes longer then the weekend for a day or two but that's it.
I'll have to look into the Binghamton pick n pull. Assuming they aren't open until spring?
Open all year, if you're crazy enough to brave the weather. No entrance fees, which is nice. Prices always seem reasonable. They have weekly weekend specials, as well.
I just looked at their website. A 95 XJ was put out one day ago., as well as several ZJs. If I was really energetic, I'd go down and see if I could get the grill I need. Alas, I'm not that energetic.
