Boost in a speed class car and drive dangerously until your boost bar is empty then it will automatically refull your boost bar which is called a burnout.
first you get a speed car nothing else just...
Hold down accelerate and left. Does not work in cars with front wheel drive (many of the Japanese ones).
Really annoyed because I wrote a great long detailed answer but it didn't save.
Depends what car you're in. You CAN'T do Donuts in the Nakamure SI-7 or the Racing edition because it is front wheel drive.
However, in most cars (and bikes) you simply hold down accelerate and...
Five - Toy Firehawk GP (unlocked by purchase), Nakamure Firehawk GP (unlocked through 100% completion), Nakamura Firehawk V4 (unlocked upon downloading the Bikes pack), Nakamura FV1100 (unlocked upon...