The phrase "souped up" is often used to describe something that has been modified or enhanced to improve its performance, speed, or appearance. Antonyms for this phrase could include "unmodified," "basic," "plain," "stock," "standard," and "unchanged." These words suggest that something has not been altered or improved in any way, and remains in its original state. They may be used to communicate a sense of simplicity, or to suggest that something is not as advanced, impressive, or interesting as it could be. For example, a "plain" car may be suggested as an antonym for a "souped up" car, or a "basic" phone may be suggested as an antonym for a "souped up" phone.