Boosters are great ways to give yourself an edge in a race. Three boosters are applied to a car, and one is applied to a race.
Cost: 100 tokens
Duration: 1 day (24 consecutive hours)
Description of booster: The double credits booster applies twice the credits you earn at the end of the race for free. Let's say you earn 5,760 credits in a Mastery race. With the Double Credits booster, you'll be given 11,520 credits instead of just 5,760! This booster is especially helpful if you are planning on purchasing a few higher-up cars.
Cost: 200 tokens
Duration: 4 consecutive hours
Description of booster: This booster is not awarded commonly, but if you manage to obtain a free one, great work! This booster gives you TWO tanks instead of just one, allowing more nitro capacity, and gifting you with a better lap time. This booster can be especially helpful with those nitro-sucking behemoths (cars with poor nitro efficiency) as some require over a tank of nitro to get itself up to speed (Bugatti 16.4 Grand Sport Vitesse, you are that one!).
Cost: 3,000-7,500 credits
Duration: 10 minutes
Description of booster: Depending on your level, you may have to pay either 3,000 credits or 7,500 credits to get this short-lived booster. At the beginning of a race, if this booster is activated, you will start with a completely full tank of nitro, rather than the tiny sliver that is rewarded at the beginning of the race. Slower accelerating cars can also benefit from this. If an extra tank is activated, the second tank will also be completely full. It's a cheap and affordable way to push yourself to the finish line.
Cost: 4,000-10,000 credits
Duration: 15 minutes
Description of booster: Every car benefits from this booster. Yes, all your stats go up ONE rank, which equates to a maximum of a 30% performance boost (27.5% when MAXed out). One way to see if you are using a tuning kit is to go to your inventory and look on the vehicle stats box on the top left, below the back button. Right next to the MAX/PRO labels, an icon with a tuning kit booster will appear and a "+##" telling you how much of a rank your car is being boosted. Now, its not a fixed rank number. The extremely rare Mercedes-Benz SLK55 AMG Special Edition has the highest tuning kit of the game, at 77 points. But the lowest tuning kit bonus in the game is the Arash AF10, at only 18 points. That is because the SLK55 AMG SE has a starting rank of a drastic 885, where it can go all the way up to 1776, without elite tuning. The Arash AF10 starts at a rank of 1692, and reaches as high as 1812.