A method of converting a diesel engine to a natural gas engine comprising inserting a spark plug into a diesel fuel injector opening in a cylinder head; installing a throttle body on the diesel engine; installing a throttle body adaptor between a throttle body and an intake manifold of said diesel engine; and modifying a piston, whereby the compression ratio of said piston is decreased during operation of said piston. The method also includes installation of a waste gate and waste gate adaptor and a timing mask.