illustrated by the cross hatched area on the diagram corresponding to 315 u00b0 of rotor rotation fig6 shows the operation of the fourth set of intermittently aligned ports as seen from a vantage point within the transfer plate cover in 45 u00b0 increments of rotor rotation a given volume of gas illustrated by the cross hatched area on each diagram is shown being compressed between 180 u00b0 and approximately 270 u00b0 of rotor rotation then being transferred past an ignition source and through the transfer plate passage 56 between approximately 270 u00b0 and 360 u00b0 of rotor rotation while expanding against the piston crown throughout the interval from somewhat after 270 u00b0 until 450 u00b0 of rotor rotation the large hole 62 connecting with the horizontal transfer passage 56 and penetrating the transfer plate in the lower left quadrant of each diagram comprises one half of the fourth set of ports and the piston expansion space 60 itself constitutes the other half it can be seen from fig6 that the conjunction of these two mating cavities occurs soon after 270 u00b0 the approximate point at which the fuel air mixture enters the transfer passage and is ignited and continues until some point after 360 u00b0 of rotor rotation both the limits and the duration of the conjunction of the fourth set of ports are determined.