It’s pretty subjective, but generally speaking a sports car is designed to drive in a “sporty” fashion: (quick acceleration, tight handling, gear ratios tuned to drive “fun”).
Muscle cars are more about just having big beefy high HP engines, tuned to have big torque, do burnouts, and have a fast 1/4 mile time.
Example: a Shelby GT 500 Mustang (muscle) vs a Porsche 911. (sports).
Latest Answers