This trick requires some starting money, a private lobby on Xbox Live,
and an online friend.

1. Buy the 1969 Chevrolet Camaro Z28.
2. Buy all engines for that Camaro.
3. Buy every part for every engine, including all aspiration parts.
4. Exit to the main menu to save the engines and parts that were
   purchased.
5. Enter the engine purchase menu, and sell every engine. *Note:*
   Do not leave the engine menu.
6. Press the Xbox Guide button, and join your friend's private lobby.
7. Leave the lobby, then quickly press B to exit to the title
   screen, with the "Press A to Start" message.
8. Enter the engine purchase menu. You will still own all the
   previously purchased engines and parts and have the money you got
   from selling the engines.
9. Repeat steps 5 through 8 as many times as desired to get an
   unlimited amount of money.