Theory 126/Engine cycle/Termination phase
Termination Is Pressure Equalisation
The claim
The cycle ends when the ratio of cylinder to exhaust pressure reaches one, so back pressure sets when the exhaust valve can open.
01Mechanism
Blowdown requires a pressure difference; the ratio sets the timing.
02Prediction
Exhaust timing should track the ratio.
03Refutation
Timing tracking crank angle alone would remove pressure.