Question: what is the difference between a 3 bar and 4 bar map sensor?
Answer: In a 3-bar sensor, you would have room for 28 psi of boost, and so on. Looking at this boost graph as an example, you see that the engine makes almost 35 psi of boost. ... That gives you a total minimum pressure range of 3.43 bar. So the minimum sensor size for this engine would be a 4-bar MAP sensor.