The boost reading that is taken by the ECU for fuelling etc
The ecu doesn't actually take any measurement of the boost pressure.
The Evo uses a mass air flow meter method to calculate air flow and fuel input.
It calculates the correct fuel input based on the air flow measured through the air meter (karmann vortex type) and the engine rpm. (plus mods for throttle angle, acceleration enrichment, engine water temperature, atmospheric air pressure, atmospheric air temperature etc)
At no time is boost pressure measured.
Other cars such as Cossies use a speed density algorithm to calculate air flow and fuel input.
By measuring boost pressure (MAP - manifold absolute pressure), boost air temperature and engine rpm the ecu calculates the density of the charge air. Knowing this and the speed of the engine the air mass flow input is easily calculated and the fuel injected accordingly.
The Evo is easy to tune as it automatically corrects for more air as it measures exactly how much is entering the engine - thus any mods such as air filter/exhaust/cams/gas flowing/more boost will not upset the fuelling until the standard injectors run out of capacity. The only thing that isn't corrected well is the ignition timing - knock sensor circuit corrects to some extent but for big boost some additional ignition timing control is essential.
With MAP sensor type ECUs if anything in the engine is changed such as air filter/exhaust/cams/gas flowing that affects the air flow characteristics of the engine the ecu cannot compensate for this increased air flow. It does not measure the air flow – only calculates the known air flow for the engine as mapped on the dyno. Improve the breathing at a particular rpm point – eg. gas flowing and the engine cannot measure this increase mass flow of air. Hence the importance of remapping/rechipping this type of ecu when modifations are made to the engine.
Boost controller will not erase fuel cut other than stopping the boost level at a particular rpm (the air mass flow) being too high for the ecu's preset parameters.
Fuel cut is there to prevent the fuel system being run beyond it's maximum.
There are cheats you can use to get around this - higher base fuel pressure/big pump/Apex S'AFC is one.
Big injectors/S'afc or HKS VPC is another.
