I want to run multiple superchargers like old aston martins used to have. I've tried, but it doesn't make more boost or power, but it does seem to have an effect of making the idle really rough, and making it want to stall.
The game doesn't support multiple superchargers, you need to simulate them as a single one, calculate what the correct values should be if you combine them etc. You can probably find some mathematical formulas on the Internet about how those values multiply with the amount of superchargers.