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Speed Limit Changer

Allows you to increase the source engine's speed limit! Go super fast! Affects every physics object!
It also allows you to change the physics gravity settings so you can make props fall into the sky, simulate zero gravity and even sideways gravity!

Description of the settings:

Air Density - Adjusts air friction (makes objects slow down over distance) I like to set this to 0
Max Velocity - Speed limit! Objects won't go faster than this
Max Ang Velocity - How fast objects can spin. Setting this too high can make objects spin out of control
Gravity X/Y/Z - Gravity along X/Y/Z Axis
Coll. Obj. Timestep - Maximum collision per object per tick.
Coll. Timestep - Maximum collision checks per tick.
Min Friction Mass - Minimum mass of an object to be affected by friction.
Max Friction Mass - Maximum mass of an object to be affected by friction.

Source: https://wiki.facepunch.com/gmod/Structures/PhysEnvPerformanceSettings