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  • More power for 4.2l

    Before the crash I thought I read something about putting a 4.0l head on a 4.2l motor. Does this really work or was I just dreaming? Also what other engine mods can be done to the 4.2l to pep it up? I've read about the Weber carb but was wondering what kind of choke does it use manual or elec. ? I have a 88 yj 4.2l 5 sp and am just starting to work on it.Any help would be appreciated.

  • #2
    Yes, it can be done. For 4.2L mods, check out Clifford Performance @ www.cliffordperformance.com. One of the top Jeep power companies. Cams, head swaps, MPFI kits, etc.

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    • #3
      I have the weber 36/38 I think thats the one I have, anyways its a built in choke you only re-attach one wire from the hunk of wires u previously had on the carter carb if I remember correctly. It did give a noticable amountt of gain in pep and pickup. I'm happy with it, and glad I went with the upgrade now I just need to make a box to go around it to keep the mud off the filter . Along with re-routing the vent tubes up into a custom snorkle *we'll see how that goes* I also want to bore it 10 or 20 over asap, that will give me plenty of power to brake stuff with 35 or 36" boggers. if you will be doing more rockclimbing with steep angles i'd shoot for the 4.0 head with fi, I just dont have alot of money atm so that will have to wait.

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      • #4
        I have the weber 38/38 and I love it gave me great pep and more low end torx. Before with the carter on the Hiway I couldnt hold a steady 65 now with the weber I can hold a steady 65-70 even on hills. It also gave alot greater controll whe offroading I havent had it stall on me once while offroading well worth easy project to do and great resualts.

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        • #5
          a 4.0 head on a 4.2 will give you 40 more horses. click this link to see the conversion step by step.

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          • #6
            I highly doubt a 4.0 will add 40HP. Maybe with the FI, but just the head - no way with a carb. If you do 3 angle valve job, port and polish it, yes. But you can do that to a 4.2 head.

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            • #7
              Originally posted by LeadFoot
              I highly doubt a 4.0 will add 40HP.
              i doubted it too initially. read the link i posted above, and talk to a few who have done the conversion. no porting/polishing/FI required (although if i went through all that trouble id sure swap on the 4.0 FI too).

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              • #8
                Are you comparing to a head with 80,000 miles on it to a new 4.0 head or new to new?

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                • #9
                  im just talking about matching a good used 4.0 head to a good used 4.2 bottom, assuming no other major problems.

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                  • #10
                    What I don't get is why didn't they do rings and such? I mean they were right there, just pull the pan off. Only an extra hundred bucks or so and they could have a engine that can go another 100,000!

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                    • #11
                      The 4.0L head has much better port design to begin with than the 4.2L. I'm not sure if there's a difference in valve sizes or not, though. So is the 2.4L (based on the Neon 2.4L) in the new TJs finally a crossflow head? That's a big killer on these engines. Heat soak from the exhaust manifold into the intake and just plain poor flow characteristics. I don't care as much abotu push rods vs overhead cams, but you've gotta have a crossflow head!!

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                      • #12
                        Originally posted by LeadFoot
                        What I don't get is why didn't they do rings and such?
                        every write up that I have found actually suggests a fresh engine when doing the head with FI swap, or atleast an engine with good oil pressure and non oil burner, and no rattles in the bearings
                        (in otherwords a rebuilt engine in my opinion)

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                        • #13
                          More Power For 4.2

                          So if I added the 4.0 head and a weber carb at the same time that would add alot of extra horses at a reasonable cost right? No cam mods would be needed? I don't want to go to the expense and labor of FI. Thanks for all the info.

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