Chainsaw Repair

Another way to look at the reasons behind the peaking of the curves:

Larger case volume means lower pressure difference and lower velocities.  Lower velocity means more time to move the air.  Therefore larger case volumes represent a time delay in moving the air.

However, port timing is always symmetrical about TDC.  So at least at lower rpm there should always be some case volume/time delay that best matches the port time events, trapping the most air before the ports close or some such (probably the transfers would be most important).

At smaller case volumes/higher velocities and higher rpm possibly inertial effects start to come into play, making the shape of the red lined plot different. 

i have not been focusing on pressure and mass flow, with this so much.  when the math came to a dead end, lost interest.  will rekindle that angle again eventually.  the fuel's mass compared to the air's is much greater.  kind of like wind trying to blow sand around on the beach.  takes a lot to get it moving because of the mass difference.  as rpm's rise, velocity naturally increases, looking just at pressure differentials may be bit deceiving because it is compressible flow.  lots of things going on.

I'm not sure there was any fuel in the tests done in this paper?  Also, the fuel is in vapor form in a engine, so its mass should just join that of the air - not quite like blowing sand.