Well first, the source engine will only let you go so fast. The limit is around 2000in/s
or around 112.5 mph. One day I was looking for some neat addons when suddenly I found:
Physics Performance and Speed Settings:
http://www.facepunch.com/showthread.php?t=585848 Which means that everything can be faster.
Things like friction,air density,gravity on any axis ,and angular velocity can be changed. (One hour a day of zero-g would be interesting)
Maybe it's a little unnessaceary, but after I hit the speed limit a few times it was a little annoying and I thought,
What would happen if we could go faster. So take this into consideration.
phys_gravity_x 0
y 0
z 0