Increased Horsepower
After buying or winning a new car, take it to the car shop before you drive it. Open up the car information screen to check your horsepower. Immediately change the oil in the car and check the horsepower again. Your horsepower level should have increased. Increased horsepower will improve your car's acceleration and top speed.
GT3 Save File Cheat
Use this cheat if you own "Gran Turismo 3" (GT3) for the PlayStation 2. Go to the main menu and find the "Saved File" options. Click on the GT3 saved file. You can then transfer the license qualifications you earned in GT3 to your GT4 game. You can also transfer up to $100,000 to GT4. Make sure you transfer everything you need, as you can only perform this cheat once.
License Guide Tip
During the countdown for the acceleration or brakes license test, press and hold "R3" just as the game starts counting down "3, 2, 1, Start." A guide will appear showing you the best route for the course, along with the best places to brake and accelerate. These guides only appear during the B and A license tests. No pace car can be present during the tests for this tip to work.
Secret Black Cars
There are four secret black cars that you can only buy during a specific time period in the game. On Day 694, two black cars will appear in both used-car showrooms. You have a week of game time to buy these cars before they disappear. It only costs $8.5 to $9 million to purchase all of the cars. These cars offer great handling, acceleration, control and speed.
Automatic Gear Trick
Automatic cars are easier to use, but they rarely have the precision of a manual car. You can freeze the gears of an automatic transmission by holding "R2." Use this trick to maintain your speed while you're going around a corner.
Easy Cash
Enter the "Special Conditions" section of the races. Go to the "Easy" races and select the second race. This is a very easy race to win. You'll earn a Toyota Rally car when you win. This car is worth $265,000. You have to race the car at least once for it to be eligible for resale. Race it on the same course and then sell it. Normally, you can't win the same car again, but if you clear your race records, you can race on the track again and earn the car back. Repeat this process to score some easy cash.