Abstract: A method and apparatus for converting a gasoline engine to a diesel engine as disclosed herein. The method involves formation of a specifically designed piston that defines a reduced combustion chamber with a reduced chamber in the cylinder head of a conventional gasoline engine and replacing the spark plug with a fuel injector. The piston includes a circular cylinder having a substantially flat end with an integral dome extending from the flat end and having an area that is more than half the area of the cylinder. The dome has a combustion chamber defined therein and the combustion chamber is in communication with the periphery of the dome adjacent the flat end of the cylinder so that movement of the piston towards the cylinder head having a reduced chamber therein will first cause the dome to enter the reduced chamber and then have the gases from the cylinder bore forced into the reduced combustion chamber to create turbulence therein.