How much HP can magnum rods take happily

Small Block Mopar Engine

  1. pishta

    pishta I know I'm right....

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    • 70aarcuda

      70aarcuda Master Hoader of SBM FABO Gold Member

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      chevy pistons valve reliefs are cut on a different angle...and they are not on center like a small block mopar
       
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      • pishta

        pishta I know I'm right....

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        Whats Chevy big end width as opposed to Mopar big end width? Get 6.0 rods and a taller piston.
         
      • nm9stheham

        nm9stheham Well-Known Member

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        You'll probably want to stick with forged for that 650 HP, just to give margin in case 'stuff happens'.

        Chevy pistons are typical shorter due to the shorter block heights.... Mopar blocks are taller than most. So it takes some time and work make thing match up.

        Small block chevy pins are typically .927" diameter, versus the larger .984" of the SBM. So you are going to have to find a way to bush the SBM rod to a much small pin. I've been figuring out a similar change in pin size and the standard rod bushings made by the hot rod manufacturers are thin-walled and don't cover that range of smaller ID to larger OD. The only thick-walled off-the-shelf bushings close to the right size (that I can find so far) are all C932 bronze, which is softer than the silicon or silicon-aluminum bronze used for performance rod bushings; those are made from C954 or C642 bronze, and for your HP use, I think the harder bronze is a necessity. So unless someone else knows of a silicon bronze thick-walled bushing close to the right size, or has some other trick, you would have to get some 1-1/8" OD x .125" wall thickness bronze tube of the right material, and have the bushing turned on a lathe. Certainly doable and the material is available.

        Bottom line is that if you are going to use Chevy small block pistons, you may be better off to use Chevy rods too, so that the pin bushing is already the right size. There are chevy rods for 2.100" journals and 2.000" journals, which require your crank rod journal to be turned down .025 and .125" respectively. The one thing I recall on most Chevy small block rods is that the big end is a bit wider (like .010" or .015" wider).

        As we say over here... there's no such thing as a free lunch LOL
         
      • maca

        maca Well-Known Member

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        Thanks heaps for the detailed information. Looks like one modification is leading to several others.
        I may need custom pistons. Is there any company you recommend for that
         
      • nm9stheham

        nm9stheham Well-Known Member

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        I think the ones recommended in the other thread are as good as you will get. Not saying you can't or shouldn't use the Chevy approach but be aware of what you are getting into. And maybe someone has a trick for the bushings.... I'd sure like to hear it!

        By the way, do you care of the pistons are down in the hole some?
         
      • maca

        maca Well-Known Member

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        I was going to Deck and do it properly for quench but I have been running this engine for 2 years with the pistons down the hole 0.035 so I could just leave it without decking to try and get compression down
         
      • skrews

        skrews Well-Known Member

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        I have run Magnum rods with ARP bolts and light pistons to around 525HP at 7200, although I wouldn't recommend anyone do it lol.
         
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        • durango r/t

          durango r/t New Member

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          Quote Rumblefish:I can’t put a finger on the ultimate hp the OE 4340 rods will take but I’ll bet that as sure as the sun rises, the rod bolts will fail first.

          I know old post but for info sake's mopar never had any oe 4340 con rods and i know fish knows that and it was just a brain fart
           
        • Locomotion

          Locomotion Well-Known Member

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          FWIW, Mopar Performance was selling 4340 rod castings pattered after 273 rods as well as 340 rods a while back. I'm at work and don't have the part #'s handy.
           
        • 70aarcuda

          70aarcuda Master Hoader of SBM FABO Gold Member

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          I think I sold you two set a few years ago..
           
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          • Ceedawg

            Ceedawg Well-Known Member

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            Good aluminum rod, at 6500 they’ll last forever
             
          • 19DART66

            19DART66 Well-Known Member

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            I had a 327 Chevy TRW forged pistons in a 360 block years ago when 360 pistons were far and few between, they had if I remember right a 1.67 comp/height and 10.5 comp. with 68cc heads. Which worked out with the 360 rods and stroke. What did not work out so good was the valve notch, with the 18 degree Mopar heads. The valve notch ended up in the thinnest part of the top of the 327 piston, seriously limited cam chooses.

            The rod bushings that were used at the time for the .927 pins were out of a International Harvester engine. Can't remember if the bushings were resized for the pins or the rods.
             
            Last edited: May 11, 2021
          • rumblefish360

            rumblefish360 So close, yet so far away FABO Gold Member

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            That be true. MoPar does have good forged OE rods though.
            Of course, these were an option....
            image.jpg image.jpg image.jpg
             
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            • m880

              m880 Well-Known Member

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              Forged like all mopars have been up till then,,imagine the 4.7l and new hemis are powder metal rods
               
              Last edited: Jun 4, 2021
            • Nat

              Nat Well-Known Member

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              that is my all time favorite A body , wish they were available in north America . great looking car
               
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