I know what it stands for (Pressure Ratio) but what is the significance? If 1.000 is perfect, what is acceptable and what is considered bad? How much variation should a well tuned car have throughout a pull? What circumstances determine PRatio?
The closer to 1.0 you are and the longer you can maintain it has a direct relashonship to how much a restriction your intake has.
From my understanding, its a measurement to help the PCM determine VE (volumetric efficiency). Basically if you're at WOT and your pratio is a 1, you're at 100% efficiency. If you're at WOT with a pratio of 75%, you have an intake restriction. If you're above 1 (boosted), you have an exhaust restriction.
Pressure ratio is actually a calculation used to determine where the engine is operating. In short, Pratio = MAP/Barometric Pressure. You will find that pressure ratio will be low when you are at idle and high when you are at WOT. The theoretical best youcan get on an NA engine is a pressure ratio of 1.0 which indicates you have no intake restriction, butthis is almost impossible to achieve due to flow restrictions in the inlet system (air intake, TB adn Intake Manifold). Boosted engines will go above 1.0 pressure ratio as they are forcing air into the engine and raising the pressure above atmospheric pressure (Hence the term Boost). J
