Regarding the spark advance and the combustion duration in the PatRoVa rotary valve:
QUOTE from http://home.people.net.au/~mrbdesign...utoTechBRV.pdf
about the Bishop rotary valve engine:
“This oblique flow through the window is responsible for one of the rotary valves most useful attributes - its strong in-cylinder tumble flow. The tumble ratio on engines with near square bore/stroke ratios is typically twice that reported for similar 4 valve engines. Unlike the poppet valve this high tumble flow is generated without any loss of volumetric efficiency (VE) and is responsible for very fast burn rates observed. Production based engines built in the early 1990’s had ignition timing of 15°, or less than half that of the best four valve engines.”
End of QUOTE
In the PatRoVa the combustion chamber (i.e. the cavity at the “top” of the cylinder head) is substantially more compact and more fatty and more concentrated around the spark plug than the combustion chamber of the Bishop rotary valve.
The high tumble flow in the PatRoVa remains strong even at the end of the compression (piston at the TDC) because of the shape of the cavity.
These characteristics make the required spark advance substantially shorter than in a Cross-Bishop rotary valve engine (and a few times shorter than in the best 4-valve engines), and the combustion ends shortly after the TDC.
For comparison with a high-tech poppet valve engine:
Think of the combustion chamber of the Ducati Panigale 1299 (116mm bore, 60.8mm stroke, 12.6:1 compression ratio (i.e. mean “height” of the combustion chamber when the piston is at the TDC: 4.5mm)) which is like a coin with abnormal top and bottom surfaces (valves, valve pockets etc).
The flame in the Panigale 1299 propagates in two only dimensions, while in the PatRoVa the flame propagates in all three dimensions.
The flame in the Panigale has to travel twice the distance it travels in the PatRoVa.
The stronger tumble, swirl and turbulence in the PatRoVa force a substantially faster flame propagation.
With the combustion completed substantially earlier in the PatRoVa Panigale, the actual expansion ratio is substantially bigger, the fuel efficiency is better, the exhaust gas temperature is lower and the power output is higher.