Instructions
Unlock the events in the Extreme Hall by winning all of the races held in the Beginner and Professional Halls. The Formula GT Championship is one of the Extreme Hall events, so you need to do this first.
Acquire the Formula Gran Turismo '04 race car by winning the Nurburgring 24 Hour Endurance race in the Endurance Hall. Like the Extreme Hall, races in the Endurance Hall can only be played once the hall has been unlocked. To do this, you'll need to finish 25 percent of the game.
Build up your computer driver's B-spec points and skill levels. This is really helpful if you want to manage the races in B-spec mode instead of racing them by hand, which can be time consuming and tiring.
Fill your car up only with as much fuel as it needs to make it between pit stops. You can figure this out by subtracting the amount of fuel you have left over at the first pit stop from 80, which is the total capacity of your tank.
Monitor the relationship between your lap pace and how quickly your tires wear down. If you consistently "push" you'll definitely gain time on the AI drivers, but you'll also be spending more time in the pits.