[KensRedZed]

It depends on how broad your idea is of the phrase "muscle car".

On this side of the pond. A muscle car in the 60's and 70's typically had a V8 that was modified to make more power.

1969 ZL1 Corvettes made 600-horsepower. Late 70's and 80's Corvettes with stock V8's were polution controlled dogs.

6-cyl Camaro = Not a muscle car.
V8 Z-28 option = true muscle car.

6-cyl Mustang = Not a muscle car.
428 Cobra-Jet Mustang = true muscle car
429 Boss Mustang = they don't have more muscle than this.