The best car in the game are
Drag=Hyundai Tib/Mustang
Circuit=Miata/AE86
That is what i found out....
I got a tiburon that can go 0-60 on dyno 2.12sec and 0-100 at 5.88sec
None of my other cars can do that.
For dragging. Try to change the ECU and Turbo configuration. Test out a little at a time.