Description of Racing cars:Modified cars
Car tuning is related to auto racing
Car tuning is modification of the performance or appearance of a vehicle. For actual "tuning" in the sense of automobiles or vehicles, see engine tuning. Most vehicles leave the factory set up for an average driver's expectations and conditions. Tuning, on the other hand, has become a way to personalize the characteristics of a vehicle to the owner's preference. Cars may be altered to provide better fuel economy, produce more power, or to provide better handling.
although most performance cars never compete. Tuned cars are built for the pleasure of owning and driving. Exterior modifications include changing the aerodynamic characteristics of the vehicle via side skirts, front and rear bumpers, spoilers, splitters, air vents and light weight wheels
Need For Speed: Carbon had the auto-sculpt feature that you mentioned. It's probably the last best street-racing NFS. There was also NFS Undercover, which is more recent and also has that auto-sculpt feature, but it's probably the worst Need For Speed game to date.
Do you want an arcade-style racer or a more simulation based one? If you want an arcade racer, NFS: Carbon and Midnight Club are your best bet. If you want something with a bit more simulation