Modern Vespa

We wanted to find out how the piston needs to be designed in order to give enough room to the transfer ports to guarantee a good situation. The piston had been constructed in a way, that the hole around the gudgeon pin close to the transfer ports could be adapted by milling.
After every little step, we put it to the test on our dynamometer to find out, which shape or which combination works best.
The original test piston was shaped like the original PX piston. So, for the red graph, the piston skirt was closed (like for a Piaggio, Polini, Grand Sport, ...).
The blue graph shows the result of the piston with a few millimetres less around the gudgeon pin. You can see such a piston on the picture above.
The green graph shows the performance with a semi-closed transfer port at the cylinder base and an adapted piston. The free space of the transfer ports in the cylinder base represents about 80% of the possible space of the cylinder.

RED GRAPH: closed piston skirt
BLUE GRAPH: semi-closed piston skirt
GREEN GRAPH: opened piston skirt

Already have one coming from Germany for my VL3. Gickspeed is building my VL3 engine, along with two wideframe motors of his own.

All I can say (without reading the thead...) is the exhaust port looks wide (good) but I dont'y like the look of the raidi of the corners.... At least looking at that pic on my phone... Looks dangerous.. I'd measure that port width and rework top two corners...