I have been playing CSR2 for a little while, and have recently defeated the Tier 1 leader, KJ. However, afterwards he challenged me to a race where I wager the gold I won from beating him for his car. I chose to take him up on it, and then I was told I'd have no hope without first getting Super Nitrous - which costs real money. So I brought it and managed to win the car from KJ.
What I want to know is, does the Super Nitrous stay, and if so what does it do... Or is it only for the races where you're racing for the cars of those you have beaten?