To increase the speed of a car, you must increase its horsepower, and one way to do this is to improve the cold-air intake on the car. Other ways to increase horsepower include installing a cat-back exhaust, high-flow catalyst and aligning the tires.
Cold air is more dense than hot air, so if trying to increase speed in a car, a cold-air intake brings more air into the cylinders. More air gives greater combustion, which can give between five and seven more horsepower to an engine.
Modifying the exhaust to a cat-back design, essentially straightening pipes, loosens up the exhaust system, which allows gases to evacuate from the system more quickly. Keep in mind, however, that newer vehicles have less restrictions than older ones, so this trick may not work as well. Another option is to install a high-flow catalyst instead of the typical catalytic converter. Remember though, it is illegal to remove an undamaged catalytic converter from a vehicle.
Modifying the tires is also an option for an increase in speed. For instance, aligning the tires in a more aggressive way can make a car more speedy. Switching normal tires for shorter ones may also help to increase acceleration.