Need for Speed Underground Cheats

First you must obtain the ''Nissan Skyline'' then you have to atleast unlocked 3/4 of all the performance upgrades(Note: Having all of them will allow you to make more money)Get rid of the performance parts that upgrade the Skyline's top speed and change the turbo package back to stock. The performance stats should read ''S, S, 3, S, S, 3, 3, 3, S''. (Or it might be different if you haven't obtained all performance parts) Then trade it in for the Mazda Miata getting a rebate of $12727 afterwards re-equip everything onto the Miata then trade it in again, this time for the Nissan Skyline getting a rebate of 119 dollars. Then just repeat the whole process again and again each time getting $12846 each time so you can buy all the Visual Parts and Performance Parts quickly.

Note: This is recommended only for progress level 95 or higher (Underground Mode only). Enemies here are much faster than you, even if you're driving an optimized car. Even playing on easy mode doesn't make much difference. So change the turbo and nitro parts to stock. For some reason, your opponents will be much slower than you.