From Bulbapedia, the community-driven Pokémon encyclopedia.
The Dash Engine (Japanese: ダッシュエンジン Dash Engine) is an upgrade for the ZERO-ONE. When installed, the Dash Engine will give the ZERO-ONE the ability to accelerate by holding the R button of the Nintendo 64 controller. Professor Oak will provide this to Todd Snap after the Valley Course is completed.
The Dash Engine greatly increases the control of the ZERO-ONE. While it does not allow it to go backwards, and the ZERO-ONE will still only stop when a Pokémon is in its way, the Dash Engine will speed up immediately, allow it to travel at an increased speed for an indefinite period of time, and return the ZERO-ONE to its normal speed as soon as the R button is released.
Though it does not allow any direct interaction with the wild Pokémon like the Pokémon food, Pester Balls and Poké Flute, it is still useful for positioning the ZERO-ONE in a desirable spot to take pictures and for moving quickly to an area of interest on a course. Also, the Dash Engine allows the ZERO-ONE to catch up to Pokémon that usually move faster than the vehicle. Pokémon which move in unusual patterns or initially appear out of photo range become accessible with usually a short burst of speed from the Dash Engine.