Do you know how your boost is stored in memory? If so open Cheat Engine, and search for the value with the correct type. If not, start with a float since that's mist likely.
Then use some boost and rescan using the new value (or reduced value if you don't know what it is). And repeat that a few time decreasing it and increasing it however you can.
Once you have it narrowed down to a few addresses (Or maybe a lot, but the number wont change), you can start changing the values and see if your in game boost actually changes. If it does, you've found the address that stores your boost.