souped-up

The story

Uncertain; the fact that the earlier senses seem to be the horse racing cant and United States Navy slang ones suggests a derivation from soup (“liquid food item”), connoting a horse or a person being filled with a liquid. Alternatively, it has been suggested that the term is a modified clipping of supe(r), with reference to an airplane or automobile engine being supercharged: see, for example, the quotation from 1925. This sense appears to post-date the horse-racing and navy slang senses.

First known use, by meaning

• from 19th to early 20th c. Of a racehorse: injected with a substance to make it run faster or to change its temperament.