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Old 01-14-2009, 07:34 PM   #1
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Swap from 4.2 to 4.0

First of all I have been in this forum for a few months and every thing I came across has a lot of info. You guys in the forum have been very helpful, Thanks.
Second, I have a 89 YJ with 4.2, Carb, and Auto trans. As you guys know it's a pain. What are some things I may need for the swap. What year 4.0 and vehicle from, and other items. Once again thanks for the help.

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Old 01-14-2009, 08:42 PM   #2
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why not jump right to a small block of some kind? i would suggest a 350 they are quite plentiful, and a few diffrent companys make the adaptors for the swap.

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Old 01-14-2009, 09:05 PM   #3
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I agree with Payj90
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Old 01-14-2009, 10:30 PM   #4
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maybe he wants to keep his jeep a jeep

4.0 is a great motor, and you'll love it compared to yours now. i'm putting a stroker built out of both motors in my 87.

i found a motor on ebay that had all the accessories, manifolds, sensors, wiring and computer, along with a radiator, and some other stuff. you'll need all that, accept the radiator.

if you want to go a cheaper route, look into the 4.0 head on the 4.2 block. you get the fuel injection basically, and your 4.2 block would stay in the jeep.
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Old 01-15-2009, 12:45 AM   #5
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What 4.0 jeep would I need to get it from? Would it be from any year and model? What about the heads, what would need for this if I would go the cheaper way.
Thanks guys.
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Old 01-15-2009, 05:06 PM   #6
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since you have a yj, i'd say any yj 4.0 91-95. now the head swap you could use any 4.0 head, do some searching cuz there's a more desirable casting number that i can't remember off hand.
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Old 01-16-2009, 01:00 AM   #7
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This sounds like you know your stuff, I will do some research and thanks a lot guys.
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Old 01-16-2009, 06:56 AM   #8
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i think 92 and up are the high output 4.0 i got mine out of a 95 cherokee you may also need either a crank posistion sensor relocator with that trans not sure but you can use any 4.0 really if you get one out of a cherokee youll need a water pump out of a 4.0 yj but that and the other stuff should be it and its mostly bolt in
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Old 01-17-2009, 11:46 AM   #9
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JPDocDave is the master when it comes to jeep issues
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Old 01-17-2009, 06:55 PM   #10
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the 350 was just a for instance, maybe he should go with a 304.
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Old 01-18-2009, 09:10 AM   #11
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JPDocDave is the master when it comes to jeep issues
i see my brain washing is working

350 is a good swap, the 304 in the old jeeps made less horse power than the 4.0 304 was like 155 hp.
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Old 01-18-2009, 11:08 AM   #12
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Swapping to a v8 is alot more entailed than just dropping in a motor, and usually presents other issues. The engine is alot heavier and will wear on suspension and steering parts that already have been worn a bit. Also you will have to mate up the transmission to whatever you use and that can be a challenge as well.

i did a 4. swap on one of my jeeps to keep the weight factor down as the 4.2 was toast. i enjoyed that motor in the jeep due to its weight to torque ratio. A jeep isn't made to run 1/4 mile engines in its stock form, most of the time you are just using the torque and that needs to be considered against the weight you are adding. The 4.2 and the 4.2 are great torque engines and the rpms don't have to be as high to use it unlike many v8's.
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Old 01-18-2009, 04:08 PM   #13
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Swapping to a v8 is alot more entailed than just dropping in a motor, and usually presents other issues. The engine is alot heavier and will wear on suspension and steering parts that already have been worn a bit. Also you will have to mate up the transmission to whatever you use and that can be a challenge as well.

i did a 4. swap on one of my jeeps to keep the weight factor down as the 4.2 was toast. i enjoyed that motor in the jeep due to its weight to torque ratio. A jeep isn't made to run 1/4 mile engines in its stock form, most of the time you are just using the torque and that needs to be considered against the weight you are adding. The 4.2 and the 4.2 are great torque engines and the rpms don't have to be as high to use it unlike many v8's.
You could always find a 440 with a 6pack and try to squeeze it in that would be one hell of a ride

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