The air intake controls the air/fuel mix going into the combustion chamber of the engine. Cars rolling off the production usually have restrictions on air flow most often a silencer, in order to reduce noise, which creates turbulence and so reduces power. For an increase in performance, the silencer should be removed or the stock part replaced altogether. In the case of cars wielding a turbocharger or supercharger, a refined air intake system is a must. In Forza, most cars, if not all, have the option of stock intake, street intake, sport intake and finally race intake.