[TESTING]Displacement having little effect in Single Cylinder

[Frankschtaldt]

139mm bore
93mm stroke
has more HP than
139mm stroke
139mm bore

139mm is a fairly long stroke.
Such an engine should produce more torque but actually producing less peak power seems reasonable to me, especially for a low quality engine.

I can see how this would seem counter intuitive but:
Power = torque x rpm
And
Torque = displacement x efficiency with stroke having some nonlethal effect.
While increasing stroke increases volume and thus generally, torque. It's combined effect on efficiency and rpm WILL reduce peak power beyond a certain length. What that length is depends on a lot of other factors.