All my research seems to suggest stuffing the crankcase will at best make the engine more powerful at higher rpm's, with a definite sacrifice in low end torque (witch in my opinion is in dreadfully low supply in these engines).
At worse you end with a
narrower power band, with no extra power anywhere to show for it.
This has to do with the velocity (speed) of gasses as they mix during the transfer phase.
The higher the gas velocity, the more efficient the scavenging process is at higher rpm, with a sacrifice in low rpm scavenging efficiency.
This is because at low rpm's, there is more time between the strokes, meaning there is more time for fresh intake gasses to mix with old exhaust gasses during the transfer phase, reducing engine efficiency at that rpm. The higher the intake gas velocity is during the transfer event, the more undesired mixing you get of intake and exhaust gasses (at lower RPM's).
At higher RPM's there simply is not enough time between strokes for this mixing to occur, so scavenging efficiency is increased (with a higher velocity transfer event). A higher velocity transfer event becomes necessary at extremely high RPM's in order to get all of the cylinder filling, and removal of exhaust gasses done in the tiny fraction of a second it has to accomplish this task. The increased bulk flow of the the higher velocity gasses is also important for high RPM power, as it helps to completely fill the cylinder with fresh intake gasses in the shorter time period available at higher and higher RPM's.
In order to preserve low rpm scavenging efficiency it is necessary not to go to far with crankcase compression.
Low end torque might even be improved by adding volume to the crankcase, in an effort to further reduce this efficiency robbing intake/exhaust gas mixing.
In order to achieve efficiency at higher rpms with this setup, it becomes necessary to increase the "time area" of the transfer and exhaust ports in order for the lower velocity gasses to be able to completely fill the cylinder in the shorter time available at higher rpms.
In this case a "boost port" is worth its weight in gold, along with widening (not raising) the exhaust port.
Sean Davis
Apollo Moto Racing
https://www.facebook.com/ApolloMotoRacing/