What is the difference between the AEM water/methanol kit with internal MAP and the Multi Input controller?

The internal MAP version (e.g. 30-3300) has a built-in MAP sensor and starts/progresses injection based on boost pressure, so it is ideal for most turbo/supercharged cars. The Multi Input version (e.g. 30-3301) accepts an external signal (MAP sensor, injector duty cycle, MAF or ECU output), which is useful for naturally aspirated engines or when you want the ECU to control injection. Tell us your setup and we will recommend the correct controller.