downshifting is similar to up-shifting but in reverse order, and is slower, at 600 milliseconds, due to the engine's electronic control unit, or ecu, needing to 'blip' the throttle so that the engine crankshaft speed can match the appropriate gear shaft speed. the car's computer senses the car slowing down, or more power required (during acceleration), and thus engages a lower gear on the shaft not in use, and then completes the downshift.