Rocker arms for 408 build

Small Block Mopar Engine

  1. Idaho

    Idaho FABO Gold Member FABO Gold Member

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    This is kind of a sticking point in planning this build.

    Szilagyi in "How to Build Big inch..." states that the stock Magnum rockers are good to about .0525" lift. I don't really see the need to go bigger. My non-ported RHS heads don't flow better above 0.500" lift. And I'm building a street cruiser that will emphasize torque over top end HP.

    I look at what's out there in the way of upgraded roller rockers and read stories of poor valve tip contact. Some great some not. I contacted the member here who makes correction kits, but these do not apply to Magnum heads. He had no suggestion for a rocker arm.

    I'm not convinced there are enough performance or durability gains with roller rockers to matter to me. Choosing to go stroker is going to put me well past the power satisfaction point. I'm confident my combo will make 450 HP / over 450 TQ with a cam in the under .525 range, and wringing the last bits out of it is not my goal. Not planning to rev past 5800 or so.

    I do want reliability. I'd like to know what folks think about this idea that the stock rockers are OK at up to .525" lift.
     
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    • moparmat2000

      moparmat2000 FABO Gold Member FABO Gold Member

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      Subscribed. I was looking at PRWs myself for my 408.
       
    • mbaird

      mbaird mbaird

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      I shimmed the stock rockers on my magnum heads to correct the geometry.
      Was it Mike @ B3 you spoke to ?
       
    • Idaho

      Idaho FABO Gold Member FABO Gold Member

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      Yes it was. Tell me more.
       
    • 12many

      12many Well-Known Member

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      There are other links that cover Magnum components and durability etc. If you had the oem magnum rocker arm set up already I’d run them, or if not and better yet I’d be looking at the Mopar Performance rocker kit if you can actually get them. They’ll be reliable I’d think with less parts involved for what you’re looking for IMO. Here’s one link with some simple thoughts on the matter that maybe others can debate as to validityMagnum Horsepower - getting all the power from your Dodge 5.2 or 5.9 engine. |
       
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      • Idaho

        Idaho FABO Gold Member FABO Gold Member

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        Rocker Arms
        Owners of LA smallblocks were spoiled for years by the old school Mopar’s use of shaft rockers. Sadly, this did not continue. On Magnum engines Chrysler opted for a pedestal rocker arm system very similar to what Ford used on 5.0 Mustangs.

        Though many enthusiasts have reservations about them, we have spun the stock rockers to 6500 RPM regularly without failure. They are stronger than they appear. For more serious racers, there are aftermarket replacements available from numerous sources, and there are kits to convert the bolt down “pedestal” style rockers to “stud mount,” enabling Magnum owners to use cheap Chevy-style stud mount rockers. Our advice is to stick with the stock stuff for anything but an all-out race effort.

        Thanks. That's one vote in favor of my current position.
         
      • mbaird

        mbaird mbaird

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        Are use some rocker arm shims that I had laying around. They were Hughes. Mike walked me through the set up
         
      • mbaird

        mbaird mbaird

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        Any kind of shim stock you can find that is the proper thickness to attain the proper centering on the valve stem should work. The ones I used were actually for shaft rockers and they were arched but I flatten them out. They just happen to be the right thickness for what I needed.
         
      • Idaho

        Idaho FABO Gold Member FABO Gold Member

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        Interesting. And confusing.
        I spoke to someone at Hughes. He was entirely unfamiliar with the very idea of shimming the Magnum rockers.
         
      • mbaird

        mbaird mbaird

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        No ... the shims were originally for shafts.. they just happened to be the right thickness and dimensions once I flattened them out.
        I will take a pic of some.
        Your application will vary depending on wether you are running a reground cam with a smaller base circle... which means you needs different pushrods.
         
      • rumblefish360

        rumblefish360 So close, yet so far away FABO Gold Member

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        I don’t see a problem with the OE Magnum rockers. The aftermarket should (key word there) have rockers that are dead on accurate in there ratio. A problem that the LA rockers have, it being a 1.5 but normally less. IDK about the Magnum rockers.

        If the Magnum rockers are not flexing and are true in there ratio, then there is no gain.
        For your goals, I think you’ll be fine.
         
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        • Idaho

          Idaho FABO Gold Member FABO Gold Member

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          Thanks Rob. If there were an option that looked like a no brainer to get good valve tip contact, I might be more inclined to go with rollers. Seems like a crap shoot.
          Spend money and hope? Doesn't really appeal.
           
        • fishy68

          fishy68 Tyr Fryr's Inc. FABO Gold Member

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          That doesn't surprise me
           
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          • fishy68

            fishy68 Tyr Fryr's Inc. FABO Gold Member

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            As long as your not running a bunch of valve spring pressure I'm with Rob that you will be fine with the stock rockers
             
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            • Idaho

              Idaho FABO Gold Member FABO Gold Member

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              The RHS heads have beehive springs.
              Install load 125.
              Open load 295.
              Rate 293.
              Seems moderate?
               
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              • 67 gt

                67 gt A Wog boy who loves his Mopars ! FABO Gold Member

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                When I had my 318 LA teen with the EQ Mags I was running the Cranes 1.6 rollers and they’re reasonably priced and I was running singles with dampeners within your cam specs . I was using the Jarmas stud girdle just for insurance.
                 
              • rumblefish360

                rumblefish360 So close, yet so far away FABO Gold Member

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                I don’t know how the aftermarket stacks up on there valve tip alignment.
                 
              • Oldmanmopar

                Oldmanmopar Going left turning right FABO Gold Member

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                You can raise the rockers or move them with shims. But you still have to set the preload or lash.

                Rockers are what usually come apart and then the pieces fall down into the motor. I have seen many of rocker pieces ruin good motors. Spend the money now or spend it later.

                I bought T&D rockers and then HTA used Crane Pushrods . When we tore the motor down the pushrods were gulled from the rockers hitting the sides of the pushrods. We now have Smith Brothers pushrods. My point is factory may be just fine if you know they are in good condition and sufficient for your build. You only get what you pay for.

                Example.. Round a bolt off with a cheap wrench. Then they go and buy a good wrench . To late the bolt is already rounded. Tinkabotit forabit. LOL
                 
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                • Idaho

                  Idaho FABO Gold Member FABO Gold Member

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                  So you do not believe factory rockers are reliable to 0.525.
                  I'm not questioning your experience but I'm wondering if the damage you've seen involved high spring pressures, high lift, high revs, or poor alignment. Any ideas on these factors?
                  The galled pushrods seems to be something caused by the aftermarket rockers. No?
                  There's always the upgraded stamped rocker to consider.
                  Do you know of a rocker that can be trusted to give good valve contact?
                  I'm not averse to spending extra where it makes sense. I just need to see that it really does.
                   
                • mbaird

                  mbaird mbaird

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                  I have been running the factory rockers in my Fastback with .510 lift and upgraded springs similar to your for 3 years now. No issues....
                  I would however like to switch to adjustables because I may go solid roller on this car at some point.
                   
                • Idaho

                  Idaho FABO Gold Member FABO Gold Member

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                  I do like the idea of adjustables just to make setup easy and get the preload consistent, especially since my valve height varies by .020" or so.
                  But it seems that one might be asking for a headache with buying aftermarket when its not required for lift.
                  I can always order individual length pushrods.
                  What rockers are you considering?
                   
                • mbaird

                  mbaird mbaird

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                  I have no idea.... There don't seem to be many really good options for cheap prices... some guys talk about using Ford or Chevy rockers but I read negatives about that. I really need to do more research.

                  first I need to finish up the Dart though....
                   
                • Oldmanmopar

                  Oldmanmopar Going left turning right FABO Gold Member

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                  Here is what we just installed on a smaller hydraulic cam motor Ball & Cup pushrods . The second picture is the T&D's on a 686 solid roller motor Ball & Ball pushrods

                  20171028_133005.jpg

                  1DSCN2807.JPG
                   
                • mbaird

                  mbaird mbaird

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                  We are running Magnum heads
                   
                • Idaho

                  Idaho FABO Gold Member FABO Gold Member

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                  Kinda sad the Magnum lost the shaft rockers.
                   
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