A Cummins C8.3 heavy-duty engine has been modified for operation on propane. The engine is spark ignited with a unique combustion chamber design to allow operation at lean mixtures to provide low emissions. The engine uses a dedicated microprocessor control system that provides ignition timing, fuel injection quantity and timing, and engine speed governing functions.The controller also uses adaptive learning to speed up its response. A special turbocharger with integral wastegate gives the required boost and control over its operating range.The engine produces 187 kW at 2100 rpm with low fuel consumption and exhaust emissions.The engine is demonstrated in a heavy-duty truck used for propane delivery. In order to fit a confined engine compartment, the new fuel system was designed to fit into the same envelope as the existing diesel engine.