1 bar is for naturally aspirated engines. 2 bar is for engines with up to 15 pounds boost, 3 bar for 30 pounds boost, 4 bar for 45 pounds boost, and 5 bar for 60 pounds boost. You can use a 2 bar sensor for a naturally aspirated engine, but you will only be using half the pressure range of the sensor. 1 bar is equal to one atmosphere of pressure.
