Definition of soup up

The term "soup up" originated in the early 1900s during the golden era of hot rod culture in the United States. In particular, it gained popularity in the 1920s and 1930s. At the time, cars were powered by four-cylinder engines with a displacement of around 140 cubic inches (2.3 liters). As a means of increasing performance, hot rodders would remove the engine block's cast-iron cylinder heads and replace them with lighter aluminum ones. The catalyst for this trend was Pete Hartman, who is considered the father of hot rodding. Hartman used this modification to power his fourth-generation Ford Model T to victory in the 1923 Glidden Tour road rally. As the popularity of hot rodding grew, the term "soup up" emerged to describe the act of modifying an engine to increase its output. One explanation for the origin of the term is that the process involved "sipping up" or adding soup to an existing, stock engine to make it more flavorful. Another theory suggests that "soup up" was a contraction of "sour up," a slang term used by mechanics to denote the addition of lead or antiknock additives to "sour" an engine's fuel mixture, resulting in better performance. In any case, "soup up" quickly became a colloquialism in automotive circles, eventually entering common parlance. Today, the phrase is still used to describe modifying engines to increase performance, whether in cars, motorcycles, or other combustion engine vehicles.