Enter "PINT" as a code at the cheats screen to unlock all cars in Arcade and Custom modes.
Get a 100% completion in Career mode to unlock Prototype mods for all cars in Career mode and the Extreme Nitrous Series in Arcade mode.
Successfully complete all the series in Arcade mode, except the Extreme Nitrous Series, to unlock the Bronze, Silver, and Gold Prototype Challenge Series.
Get 1,500 respect points from all CPU characters to unlock all Prototype parts.
Get three CRX's and mod them until you have 199 hp. Let Amber, Vito, and Chief race the free sprints until they get full skills. Then, use them in a 2-2-2 or a 3-3 circuit race.
Enter any type of pink slip race. Once you select the pink slip race, remove your memory card. Select "OK" for the race, then the "No memory card found" message will appear, disabling auto-save. If you lose the race, exit back to the title screen, insert your memory card, and it will load your career with everything you had before the race (car and respect points). If you won, insert your memory card, then exit to the career screen and select "Extras" to enable auto-save. Keep doing this to get a lot of cars or sell them to get money quicker.
Set up a sprint race on your turf, then choose level 3 or 4 cars. Look at the bhp on the cars. The car with the most bhp will usually win about 95% of the time. Remove your memory card and bet all your money on that car. If the car loses, restart the PlayStation 2 to get your money back. If your car wins, you will get a lot of money. Note: If two Mustangs are racing, choose the newer one. It has a six speed transmission unlike the old one with a five speed.
On days off, host your own race. Select a sprint and choose Class 1 vehicles. You will get a Viper vs. Viper; Viper vs. Corvette Z06; or Corvette vs. Corvette, and only two drivers, Biggi and T.K. If you get the Viper vs. Corvette, put all of your money on the Viper (maximum bet of $500,000). Collect your money, and repeat. You can choose other classes, but the lower classes give you mixed car results. Generally, anything modern will beat any muscle car in a sprint. A Skyline will beat a Corvette with up to 25 more horsepower. Biggi is a better driver than T.K. Sue is a better driver than Biggi. T.K. cheats every chance that he gets. You can also use your track to get better parts. Just schedule a circuit in the class of the car you want parts for, let your crew do the driving, and use all the cash from betting on sprints to hook up your ride.
Earn 600 respect points from any CPU character. Then, call any character on your mobile phone. Race for pink slips with one of your less powerful cars. After you get there, sell it for extra money. Make sure to have more than one car in case you lose the race.
Note: This trick requires Online mode and two memory cards. When you go online, race a friend with the your best car, but have a backup on your other memory card. Race your friend repeatedly and intentionally lose. When they have a few of your good cars, have them sell the cars and bet you the money. Then, have them lose or just ask them for all the cars back and sell them yourself.
Go to the paint menu in career mode in the workshop. Highlight "Metallic" and press X. At the color selection screen, press Triangle. Go to the base color and chose one. The original base color will now be active as a metallic color. For example, if the original base coat is red, if you highlight black as the base color the car will appear as black with a red metallic coat. This does not work if the car has been repainted already.
Get a Viper GTS fully tuned and go to the oval track. Drive about 210 mph. When you are about to turn, turn the other way into the wall. Hit the nitrous and hold it while still turning into the wall. If done correctly, your car should go up and fly. You must be in the dirt part of the turn. Try using the nitrous two seconds before hitting the wall and hit the wall (wire fence) at about a 30 degree angle.
Get a Corvette Z06 and go to the test track. Start driving backwards, then go to the curb with the crane sticking over the track and drive into the dirt. You should see hardened dirt. Drive onto that until you get halfway through the hardened dirt, then drive off slowly as if you are going back onto the track. Before you get back on the track your car should start to bounce and shake. When you come out of it, your car should be badly damaged.