Boost → pressure ratio, absolute manifold pressure and estimated air-mass increase.
Type your gauge boost in psi, bar or kPa — the value over atmospheric.
Ambient pressure is ~1013 mbar at sea level; lower at altitude, which raises the pressure ratio.
Get pressure ratio, absolute pressure in all units and the approximate air-mass increase.
Pressure ratio (PR) = absolute manifold pressure ÷ ambient pressure. It is the key number for reading a compressor map: PR = (ambient + boost) ÷ ambient.
As a first approximation, engine air mass — and therefore power — scales with the pressure ratio, minus intercooler and efficiency losses. Doubling absolute pressure (PR 2.0) roughly doubles airflow.
Gauge boost is what your gauge shows (0 at idle); absolute pressure adds atmospheric (~1 bar / 14.7 psi). ECUs and MAP sensors usually work in absolute pressure.
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