Abstract: An engine modification particularly suitable for permitting an engine, which initially ran on diesel fuel (diesel cycle) to run on gasoline (Otto cycle), includes a spacer plate connected between a cylinder head and the engine block for lowering the compression ratio of the engine. The inlet gas flow is modified so that the combustion charge introduced into the cylinder through at least one inlet valve is caused to move around the combustion chamber so that, during the period of the spark, much of the charge passes close to the spark plug to thereby obtain efficient burning of the combustion charge. A spacer plate for causing the required movement of the gas being introduced is also disclosed.