Play the Jersey City Alpha Grand Prix event, which is unlocked after reaching the Star popularity level. It is located next to the Pro Racing HQ. This event always gives a loot box for completion. Keep replaying the event, as it only takes approximately two minutes to complete. Once you reach Performance Level 320, change the difficulty from Normal to Hard. On the Hard difficulty, you will earn more followers (XP) and money for each race completion. It takes a lot of replays to max out your rank, but this method allows you to earn a lot of parts, followers, and money quickly. Additionally, this method works for any event that is short.