Thanks for sharing these graphs
The graph for the one cylinder engine reflects well the half revolution (from 360 to 540 degrees) power stroke and then the negative torque required for the compression cycle. There is also a small dip in the torque to push the exhaust gases out and then torque remains slightly negative to suck the charge in.
It is also interresting to see that on the 6 cylinder engine, even if the power strokes overlap, it is not sufficient to overcome the torque consumed by the compression strokes (still some negative torque). Only as of the V8 does the instantenuous torque always remain above zero.