Supra GT500 '97, I bought the power restrictor, racing hard tires and intermediate tires.
I set the output adjustment to 92 and power restrictor to 93, PP ends up at 699.71 with racing hards equipped to start.
I set the fuel to 1 and runs laps 1-3, pit before crossing finish on lap 3, and switch to intermediate tires + fully restore fuel.
I set the fuel map to 4 and run laps 4-7 (the rest of the race). I coast a bit on the final lap, but if you don't then set the fuel map to 5 on lap 7.
Better version
Genesis G70 Gr.4, buy hard racing tires, heavy wet tires, fully customizable racing transmission, and the high RPM turbocharger.
Go to settings and adjust the transmission top speed to 300 km/h. This allows you to beat the fastest AI driver on the straights.
Start with hard racing tires. Set the fuel map to 3 and run laps 1-3 (pit before crossing the finish on lap 3).
In the pit, switch to heavy wet tires, fully restore fuel, and set the fuel map to 6 coming back onto the track.
Run laps 4 through 7 (the rest of the race) and win comfortably by 50+ seconds.
The reason why this is better is because the car sticks to the track during heavy rain and slick track laps. I ran laps just as fast during dry conditions and faster during wet. Also, I was not aware everyone didn't get the Tom's Supra for free. In that event, this version's credit investment is lower and anyone can buy the car from brand central. This is normal difficulty btw.
Alternate method is to do two pit stops. I get done in roughly the same amount of time (between 32-33 min), and win by a similar time margin.
Start with hard racing tires. Set the fuel map to 1 and run laps 1-2 (pit before crossing the finish on lap 2).
In the pit, switch to heavy wet tires, fully restore fuel, and set the fuel map to 3 coming back onto the track.
Run laps 3 through 5 (pit before crossing the finish on lap 5).
In the pit, switch to intermediate, fully restore fuel, and set the fuel map to 1 coming back onto the track.
Run laps 6 through 7 (the rest of the race).