Boost
Hold Select while choosing an area selection at the map screen. Release Select when the auto-pilot engages. Start a race, and you will be able to use a boost. This can only be done with cars that do not already have a turbo.
Switch engines
Get over 1242.8 miles (2000 km) on the odometer on a car to unlock the ability to switch engines on that specific car. Successfully complete 100% of the game to switch the engine of any car.