events of the engine cylinders 17 disk 43 may have a number of blades 47 that can overlap with a corresponding number of blades of disk 44 the disks 43 and 44 may rotate at engine speed or other speeds but may be phased relative to the rotation of the engine crankshaft 24 of engine 11 for instance there may be a partial overlap of obstructing blades 47 and 48 that result in windows 45 the amount of overlap may be indicated by a phase angle 46 between the disks the timing of windows 45 may be considered relative to engine events additional configurations of present device 12 may include one window which operates at n times engine speed where n is the number cylinders 17 of the engine 11 the window may have a time period when it is open relative to a time it is closed during each cycle of operation the cycle of operation may a fraction of the engine speed or greater it may be a pulsating window which may have a period when it is variably partially open other configurations of device 12 may provide a variable open flow area u201c window u201d that does not have operational cycles or is not pulsing another configuration of device 12 may include a u201c piston valve u201d which is configured like the intake ports on a two stroke engine which.