A simulation system for an automotive internal combustion engine is suitable for simulating an engine operation for performing a bench test for an engine associated vehicular component, such as an automatic power transmission, an automatic transaxle, a differential gear box, and so forth. The system comprises a power plant which incorporates a relatively high inertia, and means for compensating the high inertia for achieving a low inertia equivalent to the automotive internal combustion engine; an engine characteristics generator receiving predetermined engine operation parameter simulated data for deriving a control signal commanding an output torque of said power plant according to a predetermined engine output torque variation characteristic which is set in terms of said engine operation parameter simulated data, and means, responsive to a simulated engine environmental condition indicative data, for deriving a correction value based on said environmental condition for correcting said control signal.