whats better J or X heads

Mopar General Discussions

  1. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    Would those headers even work in a A body? A pick up may be.
     
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    • Garrett Ellison

      Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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      What are the header options on a ‘65 a body now? And yes, 100 octane leaded premium was the norm, with the Sunoco 260 at the adjustable octane pump being full on 104 octane capable of supporting 12.5:1.
       
    • toolmanmike

      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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      TTI, Dougs, Hooker, (I'm sure there are a few more.)
       
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      • toolmanmike

        toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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        Headman, Even the ones made by Harold (now sold by Laysons)
         
      • Go Mango

        Go Mango Never enough beer...

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        So what are the chances that a 70 swinger 340 would have J heads? If it was late production, like May 5th.
         
      • MOPAROFFICIAL

        MOPAROFFICIAL FABO Gold Member FABO Gold Member

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        Maybe, or june.
         
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        • QuickDart360

          QuickDart360 Well-Known Member

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          The headers that laysons carries flow well? I remember DVJ cuda had some on his tunnel rammed cuda and ran very well. I guess my question is are these about as good as the equal length type headers?
           
        • ir3333

          ir3333 Well-Known Member

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          no 340 came from the factory with 10:1 compression.The factory ratings allowed you build to 10.2 or 10.5:1 to be NHRA legal. An early 340 with stock 71 or 72 cc X heads when new was around 9.6:1 or a little less.
          I don't think an iron head, 10.1 : 1 340 would run very good on 91 or even 93 octane.
           
        • Go Mango

          Go Mango Never enough beer...

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          68 through 70 340 engines had 10.5:1 compression. The 71 was dropped slightly to around 10.2 or 10.3:1. Those are the factory ratings.
           
        • Jadaharabi

          Jadaharabi FABO Gold Member FABO Gold Member

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          Never ever did I see the 340 advertised as having a 9 to 1 compression ratio. The early 340 s were advertised as having a 10 to 1 compression ratio and the 72 and 73 were advertised as having an 8.5 to 1.

          What they may have actually had and what was advertised May differ. But the factory never advertised it may actually be 9 to1 even though we're saying 10 to 1.

          Have a Happy New Year.
           
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          • toolmanmike

            toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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            I would say may be to the flow. They are tubing headers and probably flow about as good or a little better than the 67-69 HP 340 manifolds. I was never a big fan of where they exit. Look "Spitfire" up in the search box. There's lots of threads and info about them.

            spitfire.jpg
             
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            • dazedand confused

              dazedand confused Well-Known Member

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              Those hedmans headers work great in mid 60's Abodies due to tight engine compartment / space between header and steering box. That front pipe on the one header has been cut and moved side ways to clear steering box same with the hole that has been patched on the side of the header . I seen an article on here some where showing how that header fits/clearance space by steering box. 280.00 compared to 600-800.00 dollars . Ill take the 280.00 headers keep the spit fires and the douges ,TTi's ect
               
              Last edited: Dec 31, 2019
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              • Mopar Wizard

                Mopar Wizard Member

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                I've never seen a 70 340 Dart with factory X heads, not saying it didn't happen just I never seen one. Every one I have ever seen has been J,U or O.
                 
              • K.O. SWINGER

                K.O. SWINGER Well-Known Member

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                My 340 swinger came with X heads it was produced in the 11th month of 69, and I believe a big reason that the x-head is more desirable is just because of the reputation of the 340 when it came out. It was still strong through 71 but began to fall off after that and still use the Jhead some people associate the lower numbers to the J head my belief is they are equal with 202 valves
                 
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                • Go Mango

                  Go Mango Never enough beer...

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                  My 70 swinger came with J heads. For damn sure.
                  I bought it from the guy that ordered it new, and he sure as hell didn't swap the heads.
                   
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