@rgaal there probably is some merit to your method, but its probably also worth pointing out some of the some other issues in model engine radial cams.
- the cam plates are actually quite simple in principle: the inner diameter with no action (valve closed), the outer diameter 'bump' dictating (valve open) throw through the rocker assembly geometry. And the ramp curve connecting these 2 features which ideally has some smooth transition curve. The transition profile is more critical on engines with smaller cylindrical cam followers that see the cam as a point tangent. The Edwards is somewhat unique in that it has a profiled follower 'shoe'. But you will notice they are in line vertically coincident to the cylinder center line vs radially outward which is maybe a bit more common on other engines.
- I used to think cam timing was super critical on these radials. But I'm now of the opinion there is actually pretty wide margin where they run well for the task s long as the timing is reasonable & proven. Part of this stems from these radials are generally lower RPM, broader torque curve outputs, not high RPM 'peaky' horsepower type engines where cam tuning can moreso influence breathing. Back in post #140 I showed a comparison of OS (methanol glow) 4-stroke timing. You can see there is actually quite a wide deviation even normalized to the same manufacturer. (I have since found data for Saito so will add that in at some point). The Edwards has a slightly different exhaust vs intake profile but many model engines are the exact same cam plate for simplicity, just positioned different relative to TDC.
- valve lash (gap between valve stem & rocker) has quite a significant effect on actual valve open/close timing at model scale. Anywhere from 0.003 - 0.010" cold gap depending on the engine. Lash reduces open duration timing by a surprising amount on model engines, so we can't really look at the theoretical cam open/close duration in isolation. This is magnified on models because because typical lash is a higher percentage of cam throw vs full size engine.
- even with identical cam timing, different methanol (glow plug) engines will fire 'whenever they want to' within limits close to TDC. Its not an ignition driven event like a spark ignition, its a function of compression ratio, fuel etc. So an 8:1 will fire slightly different than a 10:1, which is why there is a requirement to equalize CR among the cylinders heads because the Edwards has an uncompensated master rod which would result in significantly different CR's that basis alone.
So not taking anything way from your observations or cam making proposal. I'm just saying (in my opinion) fortunately its probably not as critical as one might think. Now of course you cant have a jerky motion or a radical cam without consequences, but it seems like there is quite a generous margin within reason among similar model radial engines.
