Add the "-console" command line parameter to end of the "Target" field in the "Shortcut" properties that are used to launch the game, then start the game and the console window will appear at the starting menu. Enter sv_cheats 1 to enable cheat mode, then active one of the following functions by entering the corresponding codes at the console window. Note: You can also press ~ during game play to open and close the console window.
Changes speed of game, 0.1 = 10% of original game speed, 2 = twice the original game speed
host_timescale # (default=1)
Changes the acceleration of the speed gel
sv_speed_paint_acceleration (default = 500.0f)
Changes the maximum speed obtainable from speed gel
sv_speed_paint_max (default = 800.0f)
Changes the minimum speed (in seconds) in which the portal gun shoots when you hold click. (Affected by portalgun_fire_delay)