408 Cam on the way

Small Block Mopar Engine

  1. Idaho

    Idaho Well-Known Member

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    I did not ask about finding center. That's something I'll have to get educated about. Are you saying it will be off due to the re-grind?
    I have a degree wheel. Found out I need a 9 slot chain/gear set to do a 2 degree advance. Cloyes is balanced for a fuel pump eccentric. Summit version is not. I'll likely get that one.
     
  2. Wyrmrider

    Wyrmrider FABO Gold Member FABO Gold Member

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    ask ken he will know how he had to fit your lobes on the core
     
  3. Idaho

    Idaho Well-Known Member

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    Seems odd to me. If there's some special way necessary to find center that this would not be mentioned and spelled out on the cam spec sheet?
    We spoke about degreeing the cam and nothing was said so I assumed it would be the normal process.
     
  4. Wyrmrider

    Wyrmrider FABO Gold Member FABO Gold Member

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    don't assume anything
    ken gives you two different ways to degree the cam
    on an asymetric cam the lobe tip moves to earlier than the seat timings
    so if you degree it with the tip centerline the seat timing can be retarded and vice versa
    How many times have you seen posters say "I put it iin like the instructions said at 106 but it runs better at 102"
    or something like that
    many times it more dynamic compression aka wrong cam
    othertimes it could be what you might run into here
    no problem on a semetrical lobe
    I have to ask slantsix64 and see what he fiubd iut with his Oregon HR
    wasen't for tis irus I could stop by anc see him on my way to CVS he owes me a ride and i have to retrive one of my dial indicators
    is thread was budgetbuild- maybe he says
    cheers
     
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    • Idaho

      Idaho Well-Known Member

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      Ken clarified he always uses the intake lobe to center the cam.
      Not sure why that image went sideways.
      Many things going sideways these days.

      F7C42331-9C21-40F7-8698-7C16097D3C8B.jpeg
       
    • 67 gt

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

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      Roll master vernier type will get you the 2 degrees you require . High quality sprockets and Chain set.
       
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      • Idaho

        Idaho Well-Known Member

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        I ordered a billet set with 9 keyways from Summit.
         
      • Idaho

        Idaho Well-Known Member

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        84B7D04D-E5C6-4960-9299-3F91CB6C3598.jpeg

        EB322A7E-B455-48B3-AA79-C08B704D3523.jpeg

        Working on camshaft install. I found that when installed in the zero position my intake centerline was 112, not the 106 I expected from the cam sheet. As expected the exhaust was also off at 105 rather than 110. So the camshaft is retarded. But I think I can make it smarter.
        Ken had suggested it be installed 2 degrees advanced. That would put it at 104, so I re-installed it using the keyway for 8 degrees of advance. Now the intake measures at 104, and the exhaust at 114. I was puzzled at how that worked out but I think it's right, didn't have time to look into it carefully yet.
        The lift did come out right at .321, close enough to .322 on the sheet so I'm sure I got the right cam.
        wyrmrider you were right about having to verify how it was ground.
         
        Last edited: May 15, 2020
      • mbaird

        mbaird mbaird

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        Lookin Good !
         
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        • Idaho

          Idaho Well-Known Member

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          For those wondering about the weird broom handle sticking out, I found that with a couple wraps of tape, it fit snug in the lifter bore so I could use it as a guide to get the angle right while using a pushod between the lifter and dial gauge.
          The other thing I did a iittle different, is I just installed the number one piston and connecting rod with no rings. It spins easily with one hand on the crank bolt.
          I'd like to have feedback on those valve centerline numbers.
           
        • Cal Tonsley

          Cal Tonsley Well-Known Member

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          Might need to look into it a bit more, by my reckoning and looking at the cam card, advancing the intake to 104 centreline should have the exhaust on 112. Your figures suggest that the LSA has somehow grown a degree from the cam card 108 to 109.
           
        • Idaho

          Idaho Well-Known Member

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          I imagine one degree is not a problem but I'm going to measure again.
           
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          • Cal Tonsley

            Cal Tonsley Well-Known Member

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            Good idea, especially since you’ve had to advance 8 on the gear to achieve +2 on int centreline.
             
          • Idaho

            Idaho Well-Known Member

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            I repeated the measurements. Repeatability varied by 0.5 degree so I took 4 and averaged.
            Intake centerline 103.
            Exhaust 113.
            That puts my lsa right on the expected 108.

            Next issue, I have KB-416 step dish pistons, with the raised step at 0.020" above deck. Hughes website says if they are above deck, use a thicker gasket.
            This seems quite a lot above deck to me. I set a head on lightly snugged with 4 bolts and the piston contacts at about 7 degrees before TDC.
            I also need to verify which part of the piston to measure from for compression calculation. I think it's the rim above the dish and below the step up area but hoping someone can clarify.

            717A2520-63B0-44E0-98DB-E60ECCB86A31.jpeg
             
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            • yellow rose

              yellow rose Overnight Sensation FABO Gold Member

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              I forget what heads you are running. If they are not OE iron heads with an open chamber, you need to mill off that quench dome and not run a thicker head gasket.

              If you do have open chamber heads then use them as they are.

              The only way to know for a fact what your compression ratio is requires you to do a half inch down fill and calculate the volume of the quench dome. Otherwise you’re just guessing.
               
            • Idaho

              Idaho Well-Known Member

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              Thanks.
              I have RHS heads (closed chambers).
              I'll have to get with the machinist who sold me the stroker kit and pistons. I should not be doing any milling. The machinist has already balanced the assembly.
              Am I correct thinking if I am to calculate compression using the manufacturer offset of 25 cc, I would measure from the rim below the step up?
               
            • yellow rose

              yellow rose Overnight Sensation FABO Gold Member

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              I’m not sure why you have that piston for a magnum head but it’s not correct. I’m not into running thicker head gaskets just to fix that.

              It’s difficult to measure just the positive deck height unless you do a 1/2 inch downfill. I’ll give you an example of what you do.

              You put the piston with rings and rods attached and the crank in the block and install it in the number 1 hole. Get a dial indicator and find TDC. Then measure .500 down the hole. I usually go .600 down and then put some grease around the rings to seal them and then raise the piston back up to .500 on the indicator.

              Take your graduated burette and fill the cylinder to the top. You need a clear acrylic flat piece with a small hole in it to fill it up. You can use denatured alcohol, solvent and I know some that use water with a little dish soap in it.

              Once the cylinder is full you see how much it held. So as an example I’ll use a .030 360 for the math. You simply find the volume of the cylinder by the equation of bore x bore x stoke x 12.87 and that gives the volume of the cylinder with a flat piston and no valve reliefs or anything. In this case the answer is 836.608 or 836 cc’s. If your quench pax is actually 25 cc’s, then your actual down fill would be 811 cc’s. So you know you have a 25 cc quench pad. You also need to know how far out of the deck or below the deck the piston is. For a simple example will call it a zero deck

              Now all you need is combustion chamber volume in cc’s and the head gasket diameter and thickness and you can calculate you actually compression ratio.

              So let’s say you have 65 cc heads. You head gasket is .040 thick with a 4.090 bore.

              The math is the same as above. It’s bore x bore x thickness x 12.87 or 8.6116 or 8.6 cc’s

              You now have the volume of your cylinder at BDC and you know what the actual combustion chamber volume is because it is chamber volume + gasket volume + any deck volume below deck or you subtract the number of the quench dome form your chamber volume.

              So...let’s do the math. We know the chamber is 65 cc’s and the gasket is 8.6 so that’s 73.6 cc’s MINUS the 25 cc’s for your quench dome so you have a net chamber volume of 48.6 cc’s.

              Now it is your cylinder volume at BDC divided by the cylinder volume at TDC and you’ll get your actual compression ratio.

              So in this example you have 811 cc’s at BDC.

              Thats 811 divided by 48.6 which is 16.687 CR.

              Obviously this is a high CR but I doubt the quench dome is 25 cc’s and I doubt the piston is zero deck but probably down the hole a bit.

              That’s why you have to measure this stuff. The hard part is measuring it. The math is easy. I know it’s easy because I can do it and I hate math.

              Edit: I just saw you have a dish in the piston so your down fill would be a bigger number because of the dish, so you’ll see that when you measure the down fill as the dish offsets the volume of the quench dome. And the only way to know by how much is to down fill it.
               
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              • mbaird

                mbaird mbaird

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                Who is doing your machine work ? Just curious....

                My Oregon cam was of 1.5 degrees or so as well .
                Odd
                 
              • Idaho

                Idaho Well-Known Member

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                Thanks for that. I’m going to do it.
                The pistons are recommended for closed chamber heads. Hughes sells a 408 package for magnums with these pistons. They advise a thicker gasket if necessary but don’t give limits on how much protrusion is ok.
                They were chosen for the - 25 cc factor to get the compression into the upper 9s with 61 cc heads.
                Makes me think I have short decks. To my knowledge only a .010” cleanup was done but I have to ask if they took more for some reason.
                I suspect if the pistons are milled and standard gasket used my compression will be too high.
                 
              • 512Stroker

                512Stroker We are all here because we are not all there.

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                If you shave the tops off those pistons will you have the rotating assembly re balanced?
                 
                Last edited: May 16, 2020
              • Idaho

                Idaho Well-Known Member

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                Gibsons in Spokane Valley. Recommended by a local guy who’s had them do his Mopar work.
                 
              • yellow rose

                yellow rose Overnight Sensation FABO Gold Member

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                I’ve removed that quench pad several times after guys changed heads. I for the life of me can’t remember if we had to rebalance the crank, but I would think we did. Also, because I’m old, I can’t remember how many grams comes off when you remove it. Obviously bore diameter makes a difference.

                Getting old sucks.
                 
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                • j par

                  j par Well-hung Member

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                  Dammmm AJ...
                   
                • mbaird

                  mbaird mbaird

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                  For some reason I thought you were down near Boise .
                   
                • Idaho

                  Idaho Well-Known Member

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                  Up in the panhandle. God's country :)
                  Truth is I'd like your shorter winter.
                   
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