Your Cars can be upgrade to perform better and provide you with better profits by upgrading them.
You can find the car's stage progress in the Collection list and clicking the upgrade button.
|Stage kit||Cars needed||Profit increase||Cash unlock|
|Stage kit 1||1||+0%||n/a|
|Stage kit 2||10||+10%||15|
|Stage kit 3||25||+25%||30|
|Stage kit 4||100||+50%||50|
Note: The car stage kit "profit increase" applies to all cars of that type you currently have for sale.
Example: If you create 9 cars they could be for sale at 1,000 each. After building the 10'th car "all" 9 cars including the 10'th one you built will be for sale at the new +10% sale price. Meaning 1,100 or more after quality check increase.