Looking for info on 2406782 rods

Small Block Mopar Engine

  1. DusterJoe410.4

    DusterJoe410.4 Well-Known Member

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    I found a group of 13 part #2406782 rods for sale cheap locally, the guy has them listed as 273 rods. They appear to have bushings in them which tells me they should be floating pin. What’s the difference between these and floating pin 340 rods? I’m looking to upgrade a 360 with floating pin rods so I can put some KB Hypereutectic flat top pistons in and bump up the compression. Would these work for that or is the pin a different size? Thanks for any help with this you can give.
     
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    • 408 swinger

      408 swinger FABO Gold Member FABO Gold Member

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      Pin size is the same. All small blocks had same pin size. The beam thickness is narrower on that versus the 340. They will definitely work. Lighter weight, quicker revving. Don't overdo it though. They will only last with so much compression and RPM.
       
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      • Plymouth 65

        Plymouth 65 Floorable Deplorable

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        Are 360 throw diameter the same as 273, 318, 340? 66'
         
      • nm9stheham

        nm9stheham Well-Known Member

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        Lighter... used in 273'and early 318's. Not used as factory rods in 340's. 726 grams average versus 758 grams fore the heavier rods. Not a lot of difference but it is pretty much all in the beams of the rods. Just my SWAG..... probably fine up to 325-350-375-ish HP.

        With that off number of rods (13), see if you can find out the history. If reman rods, you don't have any idea if they were rebuilt right or not. I've looked at one batch of reman rods and found the length varied by .019" over the lot of 8 !!!! I did not buy them....

        With those KB pistons, you're gonna need to re-balance that 360 crank regardless of the rods. If you get desparate for rods, consider springing for some SCAT I-beams. Good strength, and much lighter. You can then internally balancing that 360 with the lighter KB's and those lighter rods.
         
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        • toolmanmike

          toolmanmike FABO Staff Staff Member FABO Gold Member

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          Anybody have a part number book? I do. No such number. Probably a 2406785 which is a 64-69 273 and 318 to 71.
           
        • DusterJoe410.4

          DusterJoe410.4 Well-Known Member

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          Here’s a picture of the #

          05133BC0-F0C9-47F0-95B7-F678EED41C0C.png
           
        • DusterJoe410.4

          DusterJoe410.4 Well-Known Member

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          Looking at between 9:1-10:1 compression and 5500-5800 rpm with probably 300ish hp. I ran the .050 Quench dome KBs in my previous 360 with Pressed pins and stock external balance for the same vehicle and it lived for 12-15k mi and hundreds of passes at the track before I popped a ring land off one of the pistons.
           
          Last edited: Oct 12, 2019
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          • mcode

            mcode Well-Known Member

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            That a forging NO. not a part NO.
             
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            • toolmanmike

              toolmanmike FABO Staff Staff Member FABO Gold Member

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              Both are listed in the book but not in my book. Any be a omission or misprint. I have found mistakes there before.
               
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              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                That DF98MS3049 rod in the middle is a strange number
                 
              • nm9stheham

                nm9stheham Well-Known Member

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                Here is a pix of 1 of my 273 rods... PN is the same as the OP asks about.

                DSCN2564.JPG
                 
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                • toolmanmike

                  toolmanmike FABO Staff Staff Member FABO Gold Member

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                  I guess I could look at mine if the photo is big and in focus.
                   
                • toolmanmike

                  toolmanmike FABO Staff Staff Member FABO Gold Member

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                  Nope. Must have been taken with my pld flip phone. That was 10+ years ago.

                  100_4955.JPG
                   
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                  • pishta

                    pishta I know I'm right....

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                    Nice little end weight jig. I ran across mine while I was cleaning off the bench today.
                     
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                    • nm9stheham

                      nm9stheham Well-Known Member

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                      Roger. Just so you'll know......

                      Stock 360 bobweight is around 2150 grams. Changing to the KB's in a 360 is not as dramatic a change as on a 340, but you still drop the bobweight to around 2075 or 75 grams below stock. That is well outside the normal factory tolerance, which seems to have been in the +/- 25 to 30 gram range as best as we can know from reports.

                      Change to these lighter rods and the bobweight drops to around 2025 grams which is approximately 125 grams below stock. That is getting way out of line.

                      (FWIW.... All the numbers above are weighed and measured numbers, then computed for a standard 50% reciprocating weight factor, not any guessing. I use the word 'around' only because the exact numbers will vary a bit up and down across production tolerances.)
                       
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                      • nm9stheham

                        nm9stheham Well-Known Member

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                        IIRC.. on the rods, yes. But not on the mains.
                         
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                        • nm9stheham

                          nm9stheham Well-Known Member

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                          Nope to what?
                           
                        • DusterJoe410.4

                          DusterJoe410.4 Well-Known Member

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                          Thanks for the info and definitely good food for thought going into this next build.
                           
                        • nm9stheham

                          nm9stheham Well-Known Member

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                          You're welcome! Balance was always a bit of a mystery to me (I just handed the parts to the machinist!), so when I came back into Moparland a few years back, I made an effort to figure it out and gather up lots of detailed info.
                           
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                          • Garrett Ellison

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

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                            My memory is a little (or maybe a lot) fuzzy. Didn’t DC or MP market a premium set of those rods for high rpm drag race usage? Wondering if that may be a set. Also, a question for nm9stheham. if you ran the aforementioned set up in a 360, would it be better to drill or to turn down the outside of the counter weight to bring the balance back in?
                             
                          • dibbons

                            dibbons Well-Known Member

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                            I just read ten minutes ago that both 273 and 340 rods were available in a higher strength steel thru Mopar.

                            Quote from article:

                            "About 15 years ago, Mopar Performance made max-performance rods using high-strength 4340 steel; they were offered in the light forging style (273/318) and the heavy forging style (340/360), which is about 6-percent heavier than the standard forging, so let’s assume that it is 12- to 20-percent stronger than the light forging. The 4340 material offers strength increases of 65 percent, which means that the 4340 light forging could be 45-percent stronger than the stock heavy forging. These were great rods for Stock and Super Stock race cars."

                            I have never seen or heard of this availability of a stronger 273 rod. In the '70's, I polished the beams of my 273 rods smooth and then sent them out to be shot-peened.


                            Mopar Engine Performance Guide: Crankshafts and Connecting Rods - Mopar DiY
                             
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                            • greymouser7

                              greymouser7 Vagrant Vagabond “Veni Vidi Vici” FABO Gold Member

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                              @RustyRatRod used to talk about those rods, I don’t remember if he told me directly or here on FABO.
                               
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                              • RustyRatRod

                                RustyRatRod 30 Degrees Outta Whack

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                                MP used to offer them. Impossible to find now. I have two sets of the smaller, lighter rods. The old 273 and early 318 rods that are bushed for floating pins. To my knowledge though, the thing about them being stronger was a myth. I've heard that too, but my understanding was all MP did there was take the factory rods, shot peen them add new bushings and good rod bolts and weight match them. There's no argument the shot peening process certainly makes them stronger, but AFAIK, there were never any "new" forgings made. I could be wrong.....but that would have been a huge undertaking for such a small market that those rods would have represented. They were plenty strong right from the factory anyway. They would have been stronger than the Pink rods the Chevy guy all have wet dreams about the way MP prepped them anyway. Probably good for 750 HP I would imagine. I wouldn't be scared to run them at all.
                                 
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                                • yellow rose

                                  yellow rose Doctor of Thinkology.

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                                  IIRC, those rods had 7/16 bolts and not the standard 3/8 stuff. I guess I could dig out an old DC catalog and see if my memory is still somewhat intact.
                                   
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                                  • Garrett Ellison

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

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                                    Thanks for the refresher on those Rusty, good to hear the details on those again.
                                     
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