cam selection/cyl. pressure

nope. It actually has nothing to do with the mixture coming in.. Try to only consider the mechanics of the parts. Pressure in the cylinder results from a sealed cylinder meaning the intake valve closed and the piston coming up. A longer duration cam must close the valves later therefore less area swept by the piston after the valve is closed. Now, in terms of what you have... I dont think you should be having issues with pinging. The .509 is way too large for your engine and will be a turd nor to mention you wont have vacuum for brakes. The one you have should be fine. So let me ask... with that Demon... did you tune it? On the 34° of timing... what is initial timing? What rpm is it all in? Do you have the vacuum advance hooked up?