pounds per square inch
Boost Level
When people state that their car is running (say) 15 psi of boost, they're referring to the maximum constant value that occurs at full throttle. Depending on the boost control system, the car might not achieve this level in some gears (eg first) and/or at some rpm (eg third gear at peak revs). However, if the boost pressure (measured in the plenum chamber, not at the turbo compressor or anywhere else!) reaches a peak of 15 psi and then holds it at that level for at least some time, the car is said to be running this much boost.
