A method of implementing control logic of a compression-ignition engine is provided. A control part of the engine performs a calculation according to the control logic corresponding to an engine operating state in response to a measurement of a measurement part, controls a fuel injection part, a variable valve operating mechanism, an ignition part and a supercharger so that a G/F becomes leaner than a stoichiometric air fuel ratio and a A/F becomes equal to or richer than the stoichiometric air fuel ratio, while causing the supercharger to boost, and controls the ignition part so that unburnt mixture gas combusts by self-ignition after the ignition. The method includes determining a supercharging pressure P, and determining control logic defining a close timing IVC of an intake valve. When determining the control logic, the close timing IVC (deg.aBDC) is determined so that the supercharging pressure P (kPa) satisfies the following expression: P≥8.0×10−11IVC6−1.0×10−8IVC5+3.0×10−7IVC4−4.0×10−6IVC3+0.0068IVC2−0.3209IVC+116.63.