1. #1
    luvmy83jp's Avatar
    luvmy83jp is offline Junior Member
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    4.2 to 4.0 head swap

    Can Anyone who's done this let me know how they like it and was it worth it?

  2. #2
    superj's Avatar
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    Re: 4.2 to 4.0 head swap

    i have read its good but not done it myself. i have one in the shed waiting to go on but haven;t put it on yet
    I love my old jeep.

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    Re: 4.2 to 4.0 head swap

    It's only good if you recam and put in the EFI too.
    '87 Comanche 4x4 lifted 5 1/2" on 33" tires 4.0L/AW4/NP242 $3500
    Perfect combination but too small to haul my Grand Kids and wife in.


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    Re: 4.2 to 4.0 head swap

    that is why i have not done it. a guy on jeepforums said he swapped his but stayed with his carb and he was not impressed so he put back on the 4.2 head. i think the fuel injection is what actually is making the difference. i bet if you put fuel injection on your 4.2 head, it would make it a whole different engine
    I love my old jeep.

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    luvmy83jp's Avatar
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    Re: 4.2 to 4.0 head swap

    Yeah, not sure what the point is without including the EFI. That was the reason I'm interested.

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    Re: 4.2 to 4.0 head swap

    the efi? all i know is my wife's 93 with 4.0 and auto trans got 19 on the highway and my 87 with 4.5 and auto trans gets 10. fuel injection is what was giving her the mileage, i believe.
    I love my old jeep.

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    Re: 4.2 to 4.0 head swap

    I have a 1977 CJ7 I'm doing now. For the early model CJ's there is a lot of work. Fuel line issues, if keeping the EFI you have wiring harness / ECU, CPS. It's not a weekend upgrade. I'm working on the coolong ( e-fan).

    However, the benefit is dumping my 1 barrel carb, power steering, and they say 17 mi to the gallon, and more horse power. When I'm done I'll share with all.

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    Re: 4.2 to 4.0 head swap

    I swapped a 4.0 into my '83 CJ5 back in 2009, it was well worth the effort!! I made my own CPS mounting bracket, grafted in a '93 Wrangler harness, mounted a NAPA replacement fuel pump on the rear cross member and used NAPA fuel injection hose where rubber line was needed. I also ended up running a TJ airbox and tube.

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    Re: 4.2 to 4.0 head swap

    Oh yeah I bought the pilot bushing from Advanced Adapters. At first I ran the original T176/Dana 300 but last year I swapped in a Jeep T18/Dana 20 I had kicking around so I had to get a different clutch disc and pilot bushing.
    "Good Girls and Dirty Jeeps" a song by Opal Justice http://www.youtube.com/watch?v=9xRtRE45OVQ

  10. #10
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    Re: 4.2 to 4.0 head swap

    If I had the money would build 4.2 with a billet 4.0 with roller valvetrain.

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