* Specific model: The Road Runner, GTX, and Superbird all used the 426 Hemi engine, but their aerodynamics and gearing differed, impacting top speed. The Superbird, with its aerodynamic nose cone and rear spoiler, would have the highest top speed.
* Gear ratios: Different rear-end gear ratios were available, and those geared for acceleration would have a lower top speed than those geared for higher speeds.
* Tire size: Tire diameter affects the speedometer reading and the car's actual speed.
* Road conditions: Wind, incline, and road surface all affect top speed.
* Driver skill and car condition: A skilled driver in a well-maintained car might achieve a higher speed than an unskilled driver in a poorly maintained one.
While there's no official factory figure, estimates for top speed of 1969 Hemi Plymouths typically range from around 130 mph to 145 mph for the more aerodynamic models like the Superbird, with lower figures for the Road Runner and GTX. It's crucial to remember these are estimates and achieving these speeds would be extremely dangerous and illegal.
