Hello,

Am I correct in assuming the purpose of using a hemispherical  shaped head on a two stroke engine is to -lower- the compression ratio?  Ex.: Fox .35.

If a standard, flat topped piston is used in conjunction with a hemi head, I believe lower compression would result.  Perhaps there are other reasons for installing a hemi head on some engines? I imagine controlled performance rather than higher performance is the goal.

Joe

Equal, directional burn would be a benefit of a 2 stroke hemi head.  I wonder why  hemi heads aren't incorporated in more 2 stroke engine designs?  Probably more expensive and not really necessary.

Valve arrangement in a 4 stroke (automobile) hemi engine is very efficient.  It reduces valve shrouding and increases power.  Wonder if that would work on the 4 strokes we use on model airplanes?  Again, probably too expensive and would add quite a bit of weight to the engine.

Joe

Most all of the later stunt engines do have hemi heads, as well as the four strokes.