Engine tuning is the ajustment, modification or design of internal combustion engines to yield optimal performance, either in terms of power output or economy. It has a long history, almost as long as the development of the car in general, originating with the development of early racing cars, and later, with the post-war hot-rod movement. Tuning can describe a wide variety of adjustments and modifications, from the routine adjustment of the carburetor and ignition system to significant engine overhauls. At the other end of the scale, performance tuning of an engine can involve revisiting some of the design decisions taken at quite an early stage in the development of the engine.