1. 451Mopar

    451Mopar Well-Known Member

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    As mentioned, you don't want the piston to hit the head. Don't worry about a few tenths of compression ratio.

    DCR is really a re-calculation of compression ratio from the intake valve closing point, but it is used as a comparison tool more than any actual specific value.
    The DCR calculation is a bit misleading in the "Dynamic" part, the value is only correct at zero RPM, and that is if you can actually determine the exact closing point of the intake valve. Some Calculations are done using "Advertised" duration @ 0.006" (assumes the valve is closed at 0.006" of tappet lift due to valve train clearances.)
    Others with solid cams may use the 0.020" duration numbers to account for lash, and then some just use the 0.050" numbers knowing the valve is almost closed, but getting a different DCR number. As mentioned the number is really a comparison tool to gauge against other known builds. It helps determine low rpm torque, and gives some insight at to how the engine will react to different octane fuels.
    The problem is the DCR is only a small part of estimating octane requirements.
    The DCR or compression, as it relates to octane is helpful in estimating the rise in air/fuel temperature as it is compressed, but the number does not actually tell the amount of air/fuel captured, which will change with RPM. It also does not account for ignition timing, intake air temperature, engine temperature, chamber design, spark plug location, piston to head clearance, and other factors like loading, valve and seat material type, and other factors like tuning and how the engine is loaded.
    All these factors and more go into estimating how hot the air/fuel mixture can get before it pre-ignites. Think of a Diesel engine, the heat of the compresses air is what ignites the injected fuel.
    Anyhow, that is why it is used mainly to compare known combinations.

    The Basic calculations and such can be found at the Victory Library:
    http://victorylibrary.com/mopar/cam-tech-c.htm
     
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    • Green72

      Green72 Active Member

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      Great info. So more quench .040. The number that I used for DCR was from Comp cams web site for the Thumper cam that I am considering, 73 ABDC. Am I thinking correctly that the smaller that number the higher the DCR? Is there a good target ratio? I might be over thinking this!
      Any thoughts on the light weight crank option?
      451Mopar that is a great link. Thanks
       
      Last edited: Nov 4, 2019
    • BSB67

      BSB67 FBBO Gold Member FBBO Gold Member

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      Exactly. Its just another tool that might be helpful to a professional that has been using this tool with a solid baseline of experience to evaluate the meaning of the results base on a specific build at a specific location.

      Other than that, it's a bunch of amatures guessing what the tea leaves are saying based on one of three or four formula from the internet that all give different results
       
    • 451Mopar

      451Mopar Well-Known Member

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      Depends on what your doing, and your budget. We had both the ARP2000 bolt Upgrade and the Light Weight upgrade on the Trick Flow 240 headed 505" engine because it was in the budget, but really overkill for the vehicle it is going into.
      If it is in the budget, why not? Lighter weight rotating/reciprocating assembly should not stress the block as much as a heavier assembly. In theory the lighter weight should make slightly more power, but in most street / under 6,500 RPM applications I doubt you would notice. For me the lighter weight would be to enhance the blocks durability more than increase power.

      The earlier the intake valve closes, the higher the DCR, so smaller cams make more DCR at the same rated compression ratio.
      That is why a "High performance" engine with high compression and large cam, can end up with the same DCR as a low performance, low compression engine with a small cam. Power wise, DCR only helps estimate low RPM torque mostly for street cars with tight converters and high (low number) gears.
      Many strip cars will have a much larger cam for the compression ratio which is fine when using a high stall converter, the loss of low end torque is not an issue as the engine is only at low RPM at idle. The reason, is they don't want to intake valve to close too early. At high RPM the speed on the intake charge has a lot of inertia, and leaving the valve open a bit longer can capture more air/fuel for more power (at a higher RPM.) This is how engines can have over 100% V.E.
       
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      • Curiousyellow71

        Curiousyellow71 Well-Known Member

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        Imo I would try to keep DCR under 7.5>7.0 at .006 lift. Fuel injected can help manage a higher dcr but in the heat of the summer getting a extra few hp when its cool and having it rattle when it's hot isn't really worth it to me. You can lower your static compression, widen the cams LSA or obviously more duration to change DCR, or retard/advance. Also... degree the cam in or it's all a waste of time to figure.

        What site I use:
        http://www.wallaceracing.com/Calculators.htm

        It's a good idea to mention what calc you used when you mention a dcr. Like said: apples and oranges
        Lighter rotating parts let the engine wind up faster and I agree should be easier on the block. But for a street build I doubt you will notice much difference. I'd probably look at more premium rotating assembly before buying a lesser quality thats light.
         
        Last edited: Nov 5, 2019
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        • not so famous bob

          not so famous bob Well-Known Member

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          Boy, guys are al over the place on this !
          zero deck , use a cometic .039 thick head gasket. If ur at 9.72 it should be zero , with a 7.1 rod/.250 stroker crank/piston kit.
          Ur cam will depend a lot on ur power accessories and needed vacumm. The xr292 solid roller wont have enough vacuum for you , most likely. I would call hughs engines and talk to them before buying anything , their "race'' balanced stroker kits idle like a sewing machine as far as vibration. I have a 440/505 in my 68 fastback on a motor plate ,w/ a solid street roller , and cant even feel it idleing.
          I run .037-.039 squish w/ the cometic gaskets and raised port aluminum heads.
          You "will'' need more than 2000 stall speed in ur convertor . I have 35-3800 in mine , could be a hair titer for my taste in a street car, but works well.
          Traction will be ur problem , the heads u mentioned are gonna be a h.p. killer on it tho.
          If u ever go to fuel inj. , u might not want that big of a cam either , I had to downsize my cam to get my f.i. to work right ---------jmo--
           
        • Curiousyellow71

          Curiousyellow71 Well-Known Member

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          Not sure I disagree with much of anything your sayin' not so famous Bob.
          I would think any rotating assembly should be smooth when its balanced...especially when someone with experience does it.
          I have no problem using the cometic head gaskets you mentioned, they would be a good choice .001-.003 less then .040 is not much difference. I know some go tighter yet but it's not in my comfort zone, especially on someone's first build. Better off a little conservative to me....Most the numbers I am using hopefully reflect that.

          Cam he wants to use is a hydraulic roller not the 292 solid roller.

          Like suggested...in reality DCR is a good way to play with the combination on your own project and find what works. It is not a one size fits all thing. Taking someone else's numbers and trying to use them may not go well. This op isn't far from me...similiar elevation and gas so I hope mentioned dcr numbers are helpful, but it may not. There may be more hp on the table with a higher dcr or someone may be adding more piss in the pipeline and you need lower. There is only one way to find out and build it.
           
          Last edited: Nov 5, 2019
        • Green72

          Green72 Active Member

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          i can't tell you guys how much i appreciate the info!! This could all be totally over whelming without your help. I'm actually having fun planning this project.
          Not so famous bob what makes you say that the heads will be a HP killer?
          I will call Hughs for sure they keep coming up. Not trying to sound like a dick but budget is not an issue with this build (i earned it) so a premium rotating assembly is in the cards.
           
        • Green72

          Green72 Active Member

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          i can't tell you guys how much i appreciate the info!! This could all be totally over whelming without your help. I'm actually having fun planning this project.
          Not so famous bob what makes you say that the heads will be a HP killer?
          I will call Hughs for sure, they keep coming up. Not trying to sound like a dick but budget is not an issue with this build (i earned it) so a premium rotating assembly is in the cards.
           
        • BSB67

          BSB67 FBBO Gold Member FBBO Gold Member

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          And that would put the wrist pin in the top ringland. What's a .25 stroker? Is that a 4" stroke? Why not put in a 4.25" arm?
           
          Last edited: Nov 6, 2019
        • 451Mopar

          451Mopar Well-Known Member

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          The 440 source kit we just did was balanced OK for a mild engine like we were building. If doing a race engine, the balance could be improved upon.
          Usually the rods are within 2 grams of each other, but we had one that was 3 grams heavier (on the big end) than the lightest. We didn't bother trying to get all the rods at the same weight, just matched up the heaviest and lightest on the same crank throw. Same for matching up the slight weight differences on the pin end, but most of the pin end of the rods, pins and pistons were pretty close in weight. I think overall we were within a gram of the balanced bobweight.
          If your just going to do one or two engines, just have a trusted machine shop balance the assembly because a good scale and rod balance fixture cost more than what the shop charges to balance the assembly.
          I got no problem with the combination. The mentioned Hydraulic Roller in the 505+" (4.360" bore) engine at around 9.9:1 (zero deck the block, and use about 0.030-0.040" head gasket to set the quench distance) should be fine. I like the HV oil pump, but this latest engine has the standard volume pump and pressures are good 40-50 psi.
          The 440 source 9-way timing chain is a good value, and fits without chain slop. I'm not really sold on any specific cam button. The roller type cam button is pretty easy to install, but can make noise on the stock timing chain cover. Used the Nylon type button on this last build, but had to file notches in it to clear the timing gear bolts, but not a big deal, was pretty easy with a half round file.
          With the 440 source stroker kit, the bearing clearances were all good (this was the light weight crank, and H-Beam rods), 0.0025" on the rods, and 0.0030" on the mains. I think the one thing that was missing was the rod torque specs for the ARP/RPM2000 rod bolts. I had to go lookup the rod bolt torque specs. I think it was 75 ft/lbs.
           
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          • Green72

            Green72 Active Member

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            Great info again thanks
             
          • Green72

            Green72 Active Member

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            I finally broke out of the Analysis Paralysis!!! I order a rotating assembly. Ordered from Hugh's engines, 505 kit with 24 cc dish pistons. It was time to sh@! Or get off the pot. Next will be dealing with the machine shop. I have talked to them and feel pretty good about it.
             
          • Curiousyellow71

            Curiousyellow71 Well-Known Member

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            First thing to check at your machine shop is make sure they have a torque plate for a 440. Hopefully they do.
             
          • Green72

            Green72 Active Member

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            Just an update,
            I decided to have Hugh's Engines do the machining on the block. I dropped it off today (3 hour drive). Had a great conversation with Dave. I like the idea of have the work done by the same place I'm buy the parts from, should be easier with fewer people in the loop. I will post pics of block when I pick it up
             
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            • Green72

              Green72 Active Member

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              So I got an email from Hughes Engines today regarding the block that I dropped off. Not good news! The number 5 cam bearing bore is way out of round and was repaired with epoxy (JB weld).

              C9E62C35-6094-43E7-B29A-DDEFEE354EB4.jpeg C3DB14DF-E779-4678-8B1E-C0C7433C7906.jpeg 226C6554-DFA3-42EE-BC05-3DBAA24662A3.jpeg
               
            • wyrmrider

              wyrmrider Well-Known Member

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              how much os to fix
              .010 bearings are available or you can bore and sleeve back to stock
              or if roller cam you can go to 55mm or other
               
            • 451Mopar

              451Mopar Well-Known Member

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              Wow, I never seen that before
               
            • wyrmrider

              wyrmrider Well-Known Member

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              you just had to take that cam bearing out did you not?
              it looks like it was working fine
              rear of cam sorta just floats there anyway unlike a SBM with the oil pump and dist back there
               
            • Curiousyellow71

              Curiousyellow71 Well-Known Member

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              How the heck could that happen? Seen a cam bearing spin in the bore but too have a gap on one side...that's a new one for me too..

              Looks like someone messed up machining it. Like the mandrel slipped?
               
              Last edited: Nov 23, 2019
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