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ON i know alot of CJ guys do this but opposite. I have search all over and read alot of info and i feel i can do it but i have doubts. First off how is the power compared to the 4.0. I like torque not HP so higher torque would make me happy. Also if i put the block in my XJ (just bought it for 400 and the #1 piston is missing pieces) how do i make everything like the AC and vaccum pieces work? Is this a worthwhile swap? I have found a 4.2 with less then 50,000 miles on it and i think i can get it for a steal with a trade and some cash. Let me have it if im nuts but i would like to think it would be bennifical. ALSO i dont have the money to stroek and rebuild the 4.0 so thats why this option is here. I also have the ??7120?? head (the best one), intake, TB and fuel rail. Thanks

Cole
 

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The 4.0 and the 4.2 blocks are EXACTLY the same and you will gain NOTHING by switching blocks..

The Difference:
The 4.0 has a shorter throw in the crank and a longer rod where the 4.2 has a longer crank stroke and a shorter rod.. either rod will connect to either piston too =p
The 4.0 is a multiport fuel injection motor vs the 4.2, some were carb and some where throttle body i believe.
The H.O. 4.0 cylinder head is different in some way not sure though.. i just know its better haha.

I have done a TON of research on this and you can take a 4.2 crank and rod and put it in a H.O. 4.0 Long block with the 4.0 pistons i believe to make a multport fuel injected 258..

If i were to do it, I would use a '91 or newer long block, a 258 crank, the longer 242 rods and custom pistons to make a 4.5L standard bore, 4.6L .030 over bore, 4.7L .060 over bore, I've even seen 4.8L .090 over.. Now horsepower... this has many other factors like intake, exhaust, what compression ratio pistons you run, what gas you run, and a ton more.. but on average.. these setups push 275-350 HP easily vs the 190 HP stock 4.0... as for torque... ive heard so many numbers and they're all over the chart but i've hear 300ft lbs, 400lbs, and 800lbs from some blah blah crack head dude at autozone..

Now.. I HAVE NOT BUILT A STROKER YET lol but as this is what many many months of reading several forums got me =) hope its a use to ya!!
 
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