An engine management system for an internal combustion engine. The engine management system comprises an engine control system calculating an engine operating control value, a palm-size computer transportable relative to the engine control system, and an external computer communicating with the palm-size computer. The engine operating control value is adapted to be supplied to the internal combustion engine to vary engine performance. The palm-size computer has height, width, and thickness dimensions that are no larger than approximately 6 inches by approximately 4 inches by approximately 1 inch. The palm-size computer runs a set of engine management tools that communicate engine management data to the engine control system. The external computer downloads to the palm-size computer engine management tools and engine management files, and uploads from the palm-size computer engine management files.