if it is a nasty metal burning smell you are probably burning your brakes...often smelled when new rotors are put on and you can watch them smoke...freaky the first time you see it. If they are new brakes you are more than likely burning off a layer of film from the rotor.

if you want to really test what is causing the smell push the car HARD, and let the engine slow itself down and shift down gears...no smell then more than likely your brakes. (obviously do the same thing and slam on your brakes the way you do)...smell and you probably found your problem.

hope that helps