marauder / media
Pages 32 and 33 (English rules section): wrote:
Booster: This is a request that can always be made during the race, but once per turn: ...
Brake: this request can only be made, once per turn, when the driver has finished all his sharp brakings.
Yes, you have unlimited access, but it's risky! You get faster with the booster, but your car can get damaged and you have to deal with more momentum the following turn. Braking can spin your car around and worse!
Hope that helps!