Pointer on the degree wheel: crank angleChamber, sawn open along the axisRuler mark: 830 mm, port to mid-baffleWhen the piston uncovers the exhaust port at 85° the pulse enters the pipe at about 510 m/s. The diverging cone reflects it back inverted — suction that helps empty the cylinder while the transfers are open — and the converging baffle sends back a compression wave. The port shuts at 275°, so the plug is only useful if it gets home first: 830 mm each way takes 3.3 ms, which is 180° of crank at 9,217 rpm. Rev past that and the port shuts before the wave; below it the wave comes back while everything is still open. Motion is slowed about 150×; the cones' continuous reflections are drawn as single waves.