There are various theories about the origin of the term "hot rod". The common theme is that "hot" related to "hotting up" a car, which means modifying it for greater performance. One theory is that "rod" means roadster, a lightweight 2-door car which was often used as the basis for early hot rods. Another theory is that "rod" refers to camshaft, a part of the engine which was often upgraded in order to increase power output.
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