From Wikipedia
Power System - KITT is powered by the Knight Industries turbojet with modified afterburners and a computer controlled 8-speed turbodrive transmission. Specifications 0–60 mph in 2 seconds, standing to quarter mile 4.286 seconds. Electromagnetic hyper-vacuum disc brakes: 14 foot (4.25 m) braking distance (70–0 mph - 112–0 km/h).
Turbo Boost - Used in most episodes, a series of rear mounted undercarriage rocket motors allows KITT to accelerate to incredible speeds in excess of 200 mph (322 km/h).
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Super-Pursuit Mode - KITT's Super-Pursuit mode was added at the start of the fourth season. It was the result of a redesign of the car to integrate new concepts consisting of improved rocket boosters for enhanced acceleration, retractable spoilers for aerodynamic stability, and movable air inlets for increased cooling. Super-Pursuit Mode provided a 40% boost in speed beyond the car's original top speed of 300 MPH. First used in Episode 70, "Knight of the Juggernaut, Part II".