Inherent design of the car.
My guess would be your gearing is not set correctly.
Widest does not equal Best.
Usually middle of the range is good. Try setting each one at 31, and doing some testing. You'll notice more acceleration, and better cornering. Remember, you have to slow down to take a corner.
483hp and you consider it slow. I'm guessing that you are pushing near 170mph on test course. Take a moment and think about that. In real life when have you driven 170? If you want speed try "Extreme G3" where you can break the sound barrier.
I know this sounds very negative, but 5 minutes of fore-thought would have given you a good answer.
Three of the simplest things to improve lap times. Bottom out your suspension, set Autogearing between 24 and 35, and ASM=0;TCS=1. Until you start racing for hundreths,a nd thousandths of a second, this will do fine.
Tire choice can shave 10 seconds off a lap. Suspension and gearing will make more of a difference than the next turbo stage.
Another fine point for this forum is proper english. It makes a great difference in response when you clearly state you question or thoughts.
By the way, Welcome abord. It's likely one of the best forums you'll find.
AO
Neon beat me to it.