Here is what I do: -borrow another PSP from a friend at work -create an adhoc race (Professional) -create X number of laps. -choose a course (Test Course) -choose Veyron/Enzo (or any fast car available on both garage) on both PSP -leave it on Auto Pilot so the AI can race themselves -then get back after a few minutes and do it all over again. I accumulated 9 million credits doing this. But I noticed that some races don't have a Jackpot race so I don't get a multiplier. Give it a try!