There are 3 kinds of boosts: NITRO STARTER: The Nitro Starter boost fills the nitro bar at the start of all races for a limited time. TUNING KIT: The Tuning Kit boost improves the performance of all the cars for a limited time. (The effect is equivalent to that of buying one upgrade of each type). EXTRA TANK: When enabled, it doubles the quantity of nitro your cars can hold. Activate the Nitro Starter booster as well and start all the races with a full double-nitro bar!