Desktop dyno question

Small Block Mopar Engine

  1. Backally

    Backally FABO Gold Member FABO Gold Member

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    Just got DesktopDyno 5. Figuring it out, but for those of you that have it I got a question. I have 9.5/1 compression, and Edelbrock RPM heads which list a 63cc chamber. The program only lets me put in the compression ratio, then figures out the combustion space at 98cc. Is that correct? Or since the ratio is correct does it matter?
    Thanks
     
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    • ITSAH

      ITSAH New Member

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      It is taking into account the volume of the head gasket, valve reliefs, and any space you have between TDC of the piston and the deck as well as factoring in the bore size of the cylinder so 35cc's seems a little big to me for a small block but it all depends on your combination.

      Thanks, Steve Havens
       
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      • pishta

        pishta I know I'm right....

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        Put in a custom stroke to get the head CC where it needs to be for 9.5:1.
         
      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        I've been tryin to find another free download. They just don't seem to be out there anymore. lol
         
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        • Cuda416

          Cuda416 FABO Gold Member FABO Gold Member

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          Anyone have an opinion on how much better 6.x is versus 5.x? I'm thinking of making the purchase.
           
        • Backally

          Backally FABO Gold Member FABO Gold Member

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          would it make much of a difference in the hp/tq numbers? If the compression ratio is correct, would the compression space matter?
           
        • pishta

          pishta I know I'm right....

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          so it just asks for stroke, bore and head style? That's missing a key component...cc size! Is DD5 downloadable or is it payed for? I know the original DD was posted here by me about 15 years ago, came on 1 1.44Mb floppy disk. Can you put in open or closed chamber heads? ie 302 (273 size) would be closed and 915 (360) would be open. Edelbrocks can be either (340 are 'open' for +.018 piston relief)
           
        • yellow rose

          yellow rose Overnight Sensation FABO Gold Member

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          Don’t get confused here. I think DTD is correct. What it’s telling you is the actual volume of the combustion space (actually the chamber because the piston is the actual bottom of the chamber) when the piston is at TDC. I hate maths so I keep it simple.

          If you have a 100 cc chamber, and a 10 cc dish piston and the piston is down the bore .020 and that adds another 10 cc’s you’ll have a total of 120 cc’s of volume with the piston at TDC.

          That’s what DTD is telling you. And without seeing all your numbers no one can say for sure if DYD is correct or not. I suspect it’s close but I don’t know what inputs it asks you for.
           
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          • pishta

            pishta I know I'm right....

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            • Cuda416

              Cuda416 FABO Gold Member FABO Gold Member

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            • Backally

              Backally FABO Gold Member FABO Gold Member

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              it doesn’t specify dynamic or static, I punched in dynamic but your right, could be either. I may write their tech support and ask. And haven’t been able to find out head gasket thickness, so that’s a guess too.


              Your probably right, I’m probably overthinking it. Chamber is 63cc, piston is .020 out with 25cc valve relief from what I see. And really a ballpark output from it is all I really need.
               
            • Backally

              Backally FABO Gold Member FABO Gold Member

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              It doesn’t ask head cc size, and as far as what head style it’s pretty limited. You can enter flow numbers.

              I just bought it (Competition products is just down the road from me) so still learning. There may be a way to get that stuff in there

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