Shadow Car:

Find a car with someone driving down the road and stop in front of it. Enter all but the last button of the blow up all cars cheat and you should try to enter the car.*Note: You'll jump while you enter the cheat so try to aim for the driver side door when doing this. Just as you throw the person out of the car press the last button of the cheat and the car should explode. Now enter the health cheat as fast as you can to regenerate the car and you should be able to drive the blown up car around. For most cars it increases its max speed and handling a bit. To blow up a cheetah or infernus you must do it from the passenger side only. And for a few other cars you can only do this from the driver side door.