* Gear ratios: The specific gear ratios in the automatic transmission will significantly affect top speed.
* Rear axle ratio: Different rear-end gear ratios were available, and a lower ratio (numerically higher, e.g., 3.00:1) will result in a higher top speed than a higher ratio (numerically lower, e.g., 3.50:1).
* Aerodynamics: Even minor variations in body condition (e.g., alignment, tire pressure) can affect drag.
* Weight: Modifications or added accessories will change the car's weight and therefore its top speed.
* Road conditions: Headwinds and road slope will affect the attainable top speed.
* Driver skill: Maintaining consistent throttle and proper driving technique will influence the result.
While a 1964 Thunderbird with a 425hp engine *could* reach speeds well over 100 mph under ideal conditions, it's impossible to give a precise number without knowing the specifics of the individual car's configuration. Factory literature rarely publishes a top speed figure. Road tests from the era might offer clues, but they are seldom consistent. Think of it as a range rather than a fixed number.
