Instructions
Start the game and play the career mode to win cash and unlock races.
Complete the "Battle Machine" challenge in Nevada and the super promotion showdown in Chicago to unlock the "React Team Sessions," which is your first chance to take part in speed challenges.
Buy either a Ford GT ($150,000), Porsche 911 GT 2 ($185,000,) Lamborghini Murcieloga LP640 ($320,000) or Pagani Zonda F ($741,000) from the car lot. These are the four fastest cars in the game. If you do not have enough money, redo the Chicago showdown event to build up your cash.
Select "Speed Challenge" when asked to choose a race mode for the car you purchased.
Select "Customize Blueprint" and then select "Custom Upgrade" to modify your car.
Upgrade the engine, drivetrain, forced induction, suspension, brakes, tires and nitrous oxide to level three. If you have won any level four parts from winning or dominating the races, use these on your car to increase the speed even further.
Select "Body Kit" from the customization screen and then select one of the available kits to increase the aerodynamics of your car.
Move the "Zone" slider on the autosculp screen that appears to the right while keeping an eye on the top speed shown in the details section. Select "Install" after you have found the autosculp percentage that yields the highest top speed for your car. This percentage differs depending on what car and body kit you have selected.
Select "Spoiler" from the customization screen and then select one of the available spoilers to increase the aerodynamics of your car even further.
Select "Update Blueprint" to save the changes to your car.
Continue winning races during career mode to get more cash and level four performance upgrades for your car. As soon as you win a level four upgrade, use the "garage" screen to add it to your car in order to increase the performance.