Open your hacking program (MHS, CE) and attach to engine.exe, go into the shop and purchase lightvest, equip it and search for the percentage of speed the vest gives, un-equip and search for 0, repeat till you have 1-10 addresses, change them to whatever you want and freeze/lock them and there you go, speedhack. I do not know if this is detected or not but i know that it works.
Edit: You could probably do this with heavy vest to get a armor bonus as well, this is untested and may not work.