360/410 Stroker Questions

Small Block Mopar Engine

  1. Flying G

    Flying G Member

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    Greetings. I'm putting together a 360-based stroker engine with a Scat kit (cast crank, I-beam rods, KB hypers) for street use & I hope y'all can help me with some questions:
    1. What is acceptable deck height variation from cylinder to cylinder? What have y'all seen in your builds?
    2. What is maximum acceptable rod side play for this combo? Various manual/books give .014 to .017. If it matters, I'm using a Melling HV pump. Thanks.
     
  2. 70aarcuda

    70aarcuda Master Hoader of SBM FABO Gold Member

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    Has your block been squared?
    If it has not been decked to square it...the deck height can and probably will be all over the place.....
     
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    • MOPAROFFICIAL

      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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      @Flying G
      Side play isnt too important .
      Deck variants of .004-.007 are common.
      Rod lengths can work for or against that.

      It's a stacking of tolerances.
      Measure the 4 corners for deck height and measure the rods to stick the longer rods in the tallest deck reading.
      Or square the block, start over.
       
      Last edited: Sep 16, 2020
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      • Flying G

        Flying G Member

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        Yes, it's been milled flat/square by a reputable machinist. I have no way verifying, so I take him at his word.
         
      • 70aarcuda

        70aarcuda Master Hoader of SBM FABO Gold Member

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        Did you give him a deck height to cut to?....or did just square it?...

        if it is squared.....probably a few thousands is good...what is important is the front to back number and left vs right number..
         
      • gregcon

        gregcon Well-Known Member

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        A good machinist should have no trouble putting both decks within .002-.003 of each other and .002 front to back.

        I haven't measured every rod made in the past 10 years but I'd bet the deviation in rod length (of an aftermarket set) isn't more than .001" assuming you buy the rods as a set. Scat is more likely to be off than Crower, but either way....
         
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        • Flying G

          Flying G Member

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          I appreciate the replies. I think my terminology needs refining:

          I know "deck height" is used for a block's crank CL to deck surface distance.

          But my 1st question is about variation in the piston top to deck surface distance at TDC.

          Some call this piston height, but that can have several meanings, too. Thanks.
           
        • Flying G

          Flying G Member

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          If I may ask, what is your theory or experience on this? At what value would you say side play becomes important?

          My only references in this area are the factory books & Larry Shepard's book. He says .017 is max & .020 is start over - oil pressure will be too low & the excessive oil squirted on the cylinder walls will overload the oil rings. It is unclear to me if he is speaking of a street performance engine or a race engine, or if that distinction matters. Thanks.
           
        • yellow rose

          yellow rose Master Of Insanity

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          You can run .150 side clearance and it won’t make a pinch of shit of difference.

          This is another one of those long cherished lies that get repeated, even by the book writers and experts.

          Rod bearing clearances is what controls oil past the rods, not side clearance. In fact, if I only had .020 I’d be finding more.
           
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          • MOPAROFFICIAL

            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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            they are hand in hand if the connecting rod connects the piston to the crank and the crank is "Centerlined in the block"..as you put it..but the deck is taller on number 8 vs number 2 and number one is taller than number 7... then all your pistons and rods could be the same length and they would still be at diff measurements from the deck now wouldn't they...
             
          • Flying G

            Flying G Member

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            Yep, understand & agree.

            I still would like to know how much "piston deck height at TDC" variation is typical or acceptable among the cylinders.

            Or is keeping the volume above the piston the same for each cylinder more important than keeping the heights the same (yes, these are related, too)? Thanks!
             
          • MOPAROFFICIAL

            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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            You can have a variation of a few thousands and it's not going to kill the performance of the motor.
            I will say that some of the smoothest and quietest running Motors we're the ones I balanced every little thing. I have purchased rotating assemblies balanced and all, come to find out the rods very just a little...I milled the quench pads, some .048 others .046
            I dialed the chambers in even by cc and material removal on one that was 4 cc smaller than the rest..and milled.
            Port flow all within 4 cfm.
            Quietest, smoothest running most powerful small block I can remember doing.
            Many people commented on it. The .575 solid roller was stock quiet...sewing maching.

            It not the end all, just better balanced all around than most. It's more than dynamic balance..its operational balance that's important as much or more.
             
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            • Flying G

              Flying G Member

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              Thanks for your insight. I'm still in my parts mock-up & measurement phase. This discussion has given me some ideas of what else to check. Thanks!
               
            • crackedback

              crackedback FABO Gold Member FABO Gold Member

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              Unless you have a way to measure C2C on your rods, compression height of every piston and make sure the crank is indexed to a gnats ass, then any variance in deck height, you are chasing you tail for the most part. JMO

              You could mix and match parts which is what we did on Stock Elim engines to get the compression distance evened up. Just have to work with the tolerances you have and being .003 out on an engine isn't going to make a bit of difference on a streeter.
               
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              • gregcon

                gregcon Well-Known Member

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                I'll scratch that even a little deeper...imagine a guy winning a NASCAR race. He's running in front and clearly has a few more HP than every one else.

                Freeze frame the whole thing....then go take off one of his cylinder heads, mill the block .003", and put it all back together. Un-freeze it. Is he gonna fall back in the pack? Or is he gonna keep right on truckin'?

                My money says he's gonna stay in front and keep on winning.

                I'm all for precision assembly....but I also think too many guys get hung up on numbers without keeping perspective on what they mean.

                I also think precision assembly will, ultimately, have for more to do with how smoothly and engine runs and how long it lasts than total power production.
                 
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                • RAMM

                  RAMM Well-Known Member

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                  Be wary of rod length especially these I beams. Also don't let your neighbour (guru) assemble your Mopar stroker because he "built" a 350 Chev once. J.Rob

                  Eaglebentrod.jpg
                   
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                  • yellow rose

                    yellow rose Master Of Insanity

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                    That one was down the hole a bit.
                     
                  • Flying G

                    Flying G Member

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                    That's awful!
                     
                  • Flying G

                    Flying G Member

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                    That's hilarious! Not that he grenaded a cylinder, of course. But we do hav ed to have as sense of humor about these things.
                     
                  • Flying G

                    Flying G Member

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                    RAMM, I haven't assembled a small block in a while (got into motorcycle racing for a decade or two), & never one as modified as a stroker, but I'm assembling this one myself so I'll know what's going on inside. I'm taking my time, double-checking everything, & seeking guidance where needed. If it fails, it'll be on me.

                    So, what actually happened to facilitate the creation of your table centerpiece??
                     
                  • Flying G

                    Flying G Member

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                    We also have to learn to type on our tiny phone keypads. : D
                     
                  • RAMM

                    RAMM Well-Known Member

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                    Cast 4" crank broke, rod bearings that weren't narrowed, line bore wrong, cylinders tapered, etc........ Lot's of little things that guru missed. Worst part is it cracked the cylinder all the way to the pan rail just about--couldn't sleeve this 340 to save it. It was also numbers matching to his Demon. Expensive lesson. Oh well at least it's not cancer or Covid. J.Rob
                     
                  • gregcon

                    gregcon Well-Known Member

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                    When you see a rod like that, you didn't just lose a cylinder.

                    My engine? I'd toss every rod, every piston, and heavily look at the block and crank.

                    Nothing gets that wounded all by itself.
                     
                  • RAMM

                    RAMM Well-Known Member

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                    Only thing being kept is the cylinder heads, distributor, valve covers and carb. J.Rob
                     
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                    • yellow rose

                      yellow rose Master Of Insanity

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                      Yeah, that deal trashed his wallet bad. That’s truly sickening to see this. It just makes me ill, knowing this guy got screwed, and knowing that when most guys get hammered that hard, they quit and never return.
                       
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