Hint: Use Of NOS
If you install a NOS system on your car, you can tap into it by pressing the R1 button. The Nitro guage is located to the right of the dash. Once it is empty, you will need to take a pit stop to refuel it or wait for it to slowly recharge.
Submitted by Apoka2
Unlock Audi Nuvolari Quattro
Notice that after you have completed 25% of the game, you will reveive a new car, like if you've just finished a tournament. That car is the Audi Nuvolari Quattro.
Submitted by ineedspeed
Hint: Hidden Controls
There are a number of "hidden" controls in Gran Turismo 4 that will make navigating the game a bit easier.
On the main Gran Turismo Mode screen, press L1 to jump the cursor to Home, and press R1 to jump the cursor to the country of your vehicle's manufacturer.
When looking at your garage in Home, press START to bring up the vehicle settings screen.
When changing your vehicle's settings, press START to enlarge the Engine Power/Torque curve.
At the end of a series race, press START to skip the finish times and championship points screens.
During a replay, press L3 to fast-forward.
During a pit stop, press X to to stop refueling, letting you get out of the stop faster.
With the Driving Force Pro wheel, press any combination of the LEFT, RIGHT, and DOWN buttons on the D-pad to look in that direction while driving.
Submitted by MRS Street Racer
Hint: Secret Black Cars
The vehicle line-up in the used car showrooms is constantly changing. On the last week of the changing cycle--starting day 694--four secret black race cars appear in the showrooms. Two of the cars are in the Used Car Showroom I and the other two are in Showroom II, and they only appear for one week (Gran Turismo time). All four cars can be purchased for about Cr.8,500,000 total, which is an absolute bargain for these sort of race cars.
Hint: Transfer Files
If you have a save file from GT3 you can import money and licenses into GT4. You can transfer license qualifications but you do not receive the unlockable items that come with the license when you get them without importing. You can transfer money up to 100,000 dollars. This can only be done once.
Hint: Best Starting Car
To smoke the competition at the beginning of the game purchase the Mitsubishi Lancer Evolution GSR '92, on sale in the Used Car Showroom I.
Submitted by MRS street racer
Hint: Horse Power
When you buy or receive a new car, before driving it change the oil. This will increase the Horse Power of the car, which sometimes can be a pretty significant increase.
Submitted by Tom Hahn
Hint: Fast Racing For Fast Profit
Start out with any vehicle you like. When you make enough money to make your vehicle faster using the beginner hall, move over the the special conditions Hall. Defeat the first race (Rally d' Umbria) and you will receive a Cadillac CIEN '02. Get more money and put more power into your Cadillac CIEN '02 (you won't have to if you don't want to). The CIEN will gain almost 1000+ HP. Go to the second race with the CEIN in the Special Conditions Hall called Rally d' Capri. After you win that race you will get a Toyota RSC Rally Raid Car '02 which you can sell for more than $230,000+. Keep racing that race and keep making the money.
Submitted by - Da Penguin
To obtain over 260,000 credits easily just take your best car and take it into the Rally d' Capri easy in the Special Conditions hall. Once you obtain the car sell it and you get over 260,000 credits. You can repeat this over and over and soon enough you should be able to afford anything you want.
Submitted by - mclarenf14me
Enter the European Hall event 1000 Miles! I recommend either the Ginetta G4 '64 (won from Beginner Lightweight K Cup) or the Chevelle SS 454 '70 (won from American Muscle Car Championship). Enter the Cote d'Azur race (I think the last one works just the same). Make sure your car's HP is near or above 200. Put it on B-spec, 5-Push, overtake, 3x speed. Come back after a c