One of the many modifications that you can make to your car in GTA 5 is by adding a turbo. Unlike some games where the turbo functions sort of like a nitrous oxide kit or how it provides a momentary boost upon pressing a button, GTA 5's turbo works like an actual turbocharger. You can visit a Los Santos Customs shop to start modifying your car by adding a turbo to it. Each turbo kit will display how much it improves the acceleration of your car. When you're in a race, you could even hear the whoosh and whistle of the turbo in the background as it's providing a boost to the engine. Adding a turbo is otherwise a passive buff to your car. In other words, there's no way for you to interact with it physically, but it will make your car accelerate faster.