Try typing the following during the game for interesting results:
aerf - Fast acceleration and quick braking (and free life) Keep retyping it for lots of lifes.
gass - Jump to gas station with amazing average time and score
gasst - Jump to gas station and use real average time and score
bruce - Change sign on level 2 from 'Play Grand Prix Circuit' to 'Bruce Dawson Wrote This'
6outran - unknown