It's out there in the forums, but an easy way to get Cr 340,000 in 12 minutes is to go to the Premium Sport Lounge in Campaign Mode. Take the Lamborghini Huracan, use mileage points to tune the car's weight and power (reduce the weight to minimum allowable, bring the power down to where it flips over to N500) and put RSS tires on. Do the 15 Laps on Blue Moon Bay Oval. You get 109% for handicap and 50% if you go clean. You catch the front runners by lap 10, so you don't have to "rush" through the field to keep it clean. I guess you can use other cars too, but I just happened to use the Lambo. With the 4WD and RSS tires it's quite stable.