Drivable Cars

How can I change the start speed from a drivable car??
For Example I tryed to change for this = http://www.garrysmod.org/downloads/?a=view&id=126279 , I tryed to change it from [ 800 sub pack by TheDanishMaster\scripts\vehicles dmcars\sl65amg.txt is the mercedes.
If is there , what I need to change to less from start speed and maximum speed.
I changed but is not working



"HorsePower"			"621"
"MaxRPM"				"4800"
"ShiftUpRPM"			"3400"
"ShiftDownRPM"			"2500"