my friend has 2011 ford mustang (not gt) and i have a 1999 Mitsubishi galant gtz both of cars are stock and he wants to race me. will i win? and if not what part cabt

The 2011 mustang has about 110 more horses on the galant. Unless your doing like a track race with lots of turns, I dont think you have much of chance. And to be able to beat him youll be force induction (i.e. turbo or supercharger).

Find you'r self a mitsubishi galant Legnum vr-4 and use that one... tune the enginee to 500 bhp and you will crush you'r friend and anything else that comes you'r way ;)