The Impala SS had a powerful LT1 small-block V8, while the Magnum's available engines, even the 5.7L Hemi, weren't as quick off the line in stock form. The Impala SS benefits from a lighter weight and a more powerful engine for its time. While the Hemi Magnum has more horsepower, the Impala's lower weight and superior power-to-weight ratio give it a significant advantage in acceleration.