Editing Constitution Class (section)

===Propulsion systems===

The Constitution-class of starships has been fitted with both lithium and dilithium reactor circuits in the warp drive assembly over its service lifetime. The vessel's standard cruising speed was warp 6, while its maximum cruising speed was warp 8. Warp 9 was also possible for this class of starship, although it was highly discouraged because it was an unsafe velocity.

The USS Enterprise was twice modified to achieve a speed of warp 11. The probe Nomad increased the ship's engine efficiency by 57% in 2267, allowing the ship to reach warp 11, but Kirk persuaded Nomad to reverse its "repairs" because the ship's structure could not stand the stress of that much power, and would eventually destroy the ship. (TOS: "The Changeling")

More extensive modifications made to the ship by the Kelvans in 2268, who were able to produce velocities that were far beyond the reach of Federation science, allowing the Enterprise to safely maintain a cruising speed of warp 11 while traveling through the intergalactic void. (TOS: "By Any Other Name")

The maximum warp speed recorded for this class by itself was warp 14.1, achieved by the Enterprise due to sabotage to the vessel's warp drive system. While the ship itself was not structured to take that speed for any length of time, the Enterprise was able to maintain that velocity for nearly 15 minutes. (TOS: "That Which Survives")

The Enterprise also maintained stability at warp 22, while tractored to a ship going warp 32. (TAS: "The Counter-Clock Incident") 

Following the 2270s refit of the class, the Constitution was equipped with a linear dilithium-controlled MARA (Matter/Antimatter Reactor Assembly), and a pulse dilithium-controlled assembly was installed by the mid 2290s aboard the USS Enterprise. (Star Trek II: The Wrath of Khan; Star Trek VI: The Undiscovered Country)

The Constitution-class' impulse drive system was a twin-port engine, capable of velocities at least warp factor 0.8. (Star Trek: The Motion Picture) A fusion explosion equivalent to at least 97.835 megatons would result if the impulse engines were overloaded. (TOS: "The Doomsday Machine")