+1 Great explanation.
OP next time try WIKI first.
Originally Posted by Ænema
The term PSI is a bit misleading the way we colloquially use it. When we use the term "PSI" we're actually talking "PSIG"(manifold/charge pipe pressure with "0" being atmospheric pressure.)
Unless it is the Cobb guys talking in relation to Boost mean abs and Boost mean act, that's PSI. That's something I see people get confused about when looking at Cobb logs. They think 28psi means 28psig and that's not the case.