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  • Better engine 4.0 or 258 with 4.0 head

    So, I have an opportunity to pick up a 91 HO 4.0 out of an XJ. I am curious as to what the better combo would be.

    4.0 as is fuel injected

    258, which is in the Jeep and running, with 4.0 head with the 4.0 fuel injection. I know I'll need the crank position sensor mounted somewhere, but I haven't decided if I would have the bell machined or use a Hesco setup on the snout.

    Opinions????

    Don't say swap out for a 350, not going to do that.

    High5

  • #2
    From what i have heard and read either is a pretty good option. But it would be easier to put the haed and the fuel injection in. Plus you know the 258 if it is in the Jeep may be less of a gamble than a motor you dont know. But I would take the motor from the XJ and just take the parts you need, later if you want you could swap in the 4.0.

    Comment


    • #3
      newer 4.0 = better all around motor

      4.2 block with new(er) 4.0 EFI head = more power, less mpg.

      it's not too much of a different. just depends on if you want to go through all the hoop-la to conver to EFI

      Comment


      • #4
        use both and stroke it.

        Comment


        • #5
          Originally posted by GPER
          use both and stroke it.


          The stroker is your best bet for all around performance. The 258 is a good torquey motor mostly because of its relatively long stroke. The 4.0 has higher HP rating because of its larger bore. When those two mate and produce a 4.7, you have the potential to have great motor, I have heard nothing but rave reviews.

          Comment


          • #6
            I have heard the other side of the review. All I have heard is that people have a heck of a time with pinging under load. They have to run high octane fuel and even then still pinging. Plus, I don't think my wrenchin skills are up for that kind of surgery.

            With the 4.0 head conversion, does everyone just have the bellhousing machined for the crank position sensor or do they make a kit to use the front of the motor. I have heard that Hesco makes a kit, but I can't find it.

            High5

            Comment


            • #7
              Try This link:

              http://www.hescosc.com/shop.asp?acti...098&catId=7902

              Hadn't heard about pinging on the 4.7, but it doesn't surprise me, everyone I have talked to that has retrofitted the MPI to a 258 has had pinging.

              With that in mind, you can fix it before it starts by using a dish top piston and lowering the compression ratio, or Hesco may have an adjustable bracket to retard the timing just a little.

              I come from a slightly different background, so a simple rebuild doesn't scare me so much.

              Comment


              • #8
                I say watch Ebay and be patient..... I bought a TBI kit on there for my 258 a couple weeks ago at a kick *** price... complete bolt on, and alot less headaches than trying to adapt all of the 4.0 MPI stuff...... Ill also be doing a 4.0 head swap in the near future! I cant wait!!!!

                thats my $.02

                Comment


                • #9
                  From what I have read if you proper quench between the head and the block you don't have the pinging.

                  One word of caution if you go with a different cam Mopar Performance are the only valve springs that work and they are $$$$$$$$$$$$$$$$$$.

                  Comment


                  • #10
                    HMR-RSQ has the 4.0 with the 258 stuff in it, dunno how all he did it but his wont pingin when he was at my house.

                    Comment


                    • #11
                      Originally posted by UPJ Wheeler
                      I say watch Ebay and be patient..... I bought a TBI kit on there for my 258 a couple weeks ago at a kick *** price... complete bolt on, and alot less headaches than trying to adapt all of the 4.0 MPI stuff...... Ill also be doing a 4.0 head swap in the near future! I cant wait!!!!

                      thats my $.02
                      Retrofitting the MPI isn't all that tough, I did it for my brother-in-law a couple years ago. I didn't bother to buy a conversion harness, just used the stock one. Even with that it was just an afternoon project.

                      Comment


                      • #12
                        Originally posted by Mud_slinga
                        HMR-RSQ has the 4.0 with the 258 stuff in it, dunno how all he did it but his wont pingin when he was at my house.

                        And I even run 87 octane!! Used old 258 crank and rods outta my old 79 cj5
                        and had it bored had the block decked to O and used factory head gasket, with late model XJ exhaust manifold (why buy big bucks header). Used big ford injectors and had buddy up in Detriot reprogram my PCM to allow me to use my DRBII and I am now able to adjust timing and fuel on my own.
                        Stock intake, throttle body and ign. Tows the camper and runs the interstates at speeds that are un-believable. Plus I get 24-26 MPG w/o the camper. Good luck HMR-RSQ

                        Comment


                        • #13
                          Originally posted by High5
                          So, I have an opportunity to pick up a 91 HO 4.0 out of an XJ. I am curious as to what the better combo would be.

                          4.0 as is fuel injected

                          258, which is in the Jeep and running, with 4.0 head with the 4.0 fuel injection. I know I'll need the crank position sensor mounted somewhere, but I haven't decided if I would have the bell machined or use a Hesco setup on the snout.

                          Opinions????

                          Don't say swap out for a 350, not going to do that.

                          High5
                          http://www.geocities.com/035jeep/40L.html or http://www.bustedjeep.com and for more info http://www.customefis.com maybe this will help.

                          Comment

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