I'm no pro, but the only way I can think to do that is pin invisible graphics to your car, different numbers, when the car collides, check to see if any of the pieces collide with the object you hit, then spawn particles at the pinned objects location, for example 1 invisible object could be attached ( pinned) to the hood of the car, on collide check all pieces, if that piece is hitting too then particles will spawn at the invisible object on the hoods location making it look like sparks are comming off of the hood.