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Dynamic compression as guide to static compression increase with bigger cam

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  • Dynamic compression as guide to static compression increase with bigger cam

    With the same combustion chamber and similar bore and stroke, can a known pump gas friendly combination be extrapolated to allow more compression with a larger, later closing cam? I ran a number of calculations using the Wallace Racing calculator and found that the dynamic compression ratio stayed the same with the new bigger cam by raising static compression from 11:1 to 11.5:1.

    Is this over simplified?
    Drag Week 2006 & 2012 - Winner Street Race Big Block Naturally Aspirated - R/U 2007 Broke DW '05 and Drag Weekend '15 Coincidence?

  • #2
    Errr... no, its not over simplified.

    The cam controls the sunroof, right?
    Yes, I'm a CarJunkie... How many times would YOU rebuild the same engine before getting a crate motor?




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    • #3
      Originally posted by Caveman Tony View Post
      Errr... no, its not over simplified.

      The cam controls the sunroof, right?
      Ahh, yes, the cam controls dynamic compression....I've spent a long time dealing with compression. Static is just a number, usually to compensate for cam profile.
      I deal in nitro engines, but numbers are numbers, until you add fuel!
      Originally posted by TC
      also boost will make the cam act smaller

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      • #4
        LOL your on the track Bill, in fact your way ahead, its a balance, but dont get carried away because you will be changing the RPM it all comes in at too.
        2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
        First to run in the .90s .80s and .70's in SBN/A
        2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
        2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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        • #5
          We (Dougan's and me) ran this by the Comp Cam guy, and by the JE piston guy and ended up going with the 11.5:1 on the order sheet. I have another car buddy who ran 11.6 with a similar combustion chamber and a smaller cam so I have some reason feel that we are safe, but not by much.

          As to RPM the plan is to have about a 500-600 RPM higher operating range for the 'refresh' based on the longer duration and slight increase in .200 duration/lift specs. At the other end the increase in compression is also intended to help offset the loss of torque we expect at rpm ranges below the stall speed of the new converter. Drivability you know.
          Drag Week 2006 & 2012 - Winner Street Race Big Block Naturally Aspirated - R/U 2007 Broke DW '05 and Drag Weekend '15 Coincidence?

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          • #6
            Originally posted by Caveman Tony View Post
            Errr... no, its not over simplified.

            The cam controls the sunroof, right?
            Actually on mine the cam controls the convertable top.
            Drag Week 2006 & 2012 - Winner Street Race Big Block Naturally Aspirated - R/U 2007 Broke DW '05 and Drag Weekend '15 Coincidence?

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            • #7
              With a high stall converter it will be hard to lug it also. You would be very Surprised at what you can run. If you drive where its muddy and wing it up on Good fuel at the track when you play with Valve events
              2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
              First to run in the .90s .80s and .70's in SBN/A
              2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
              2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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              • #8
                FWIW, my 585" SOHC runs 13:1 static and behaves beautifully on the street on 92 octane pump gas. 6K stall converter and a big cam, something like 304 seat to seat. DCR worked out to be 8.5:1.

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                • #9
                  Originally posted by jaybnve View Post
                  FWIW, my 585" SOHC runs 13:1 static and behaves beautifully on the street on 92 octane pump gas. 6K stall converter and a big cam, something like 304 seat to seat. DCR worked out to be 8.5:1.
                  What's the LSA, figuring it's pretty wide..........

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                  • #10
                    It's 114, with the ICL degreed at 110.

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