Start a race in a car that has a smokescreen. Then when you are able to use your smokescreen, use it for as long as possible. Then when the smokescreen overheats use the "unwreck" feature to go back to the time that you are spewing smoke. Then realease the unwreck button. It might take a couple tries to get it right. You should be using the smokescreen without pressing the button. If you are, then you did it correctly.
Note: If you press the smokescreen button while it is going infinitely, the smoke will stop and you will have to do the glitch over again. I don't know if it works on xbox live because I didnt try it on multiplayer yet. All I know is that it works on campain and arcade mode.
Ok guys you always wanted a cheat to get you evrything inside the game well....i got one go into the game create a new account/name/profile and make it magicman it gets you everything unlockable in the game enjoy -busch