There are 2 different sets of codes for the car's name and body. I'm assuming U are using the name ones only since U have gotten the No Name NoName result, which does happen with some of the hidden cars. The codes for V1.2 are as follows.
Car Name
801cd558-????
801cd55a-????
Body
801cd5e4-????
801cd5e6-????
changing the ???? to the apppropriate code for which ever name/body U want. U use the same sets of part codes for each. For example to change the name and body of the car in the first slot to that of a Lancia Stratos it would look like this.
Car Name
801cd558-D798
801cd55a-1359
Body
801cd5e4-D798
801cd5e6-1359
ok...............i want to know how to put on new chassis or bodys on your car to have a different car! i keep typin in the codes...........they just dont work........could someone give me an example code to put in! i have version 1.2! i can get everything else to work.............but not getting a new body!!! how do u do it!? sometimes the car name says......."no name no name" ! 
.............................THX 4 the help
