Originally Posted by Bosch-Man
...i have a swedish plenum so that accounts for the -2psi defficit on my gauge to his
...i know it aint accurate the fooking boost gauge told me that i was merely asking as i want to make sure my vaccuum is correct.
Phil,
I wasnt joking.
Due to the large internal volume of the plenum you get pulses of air
at low rpm. This is measured by the map sensor and averaged.
The result is that the ACTUAL cyclinder charge pressure will be different
on that the map sensor as it reacts much quicker.
Mechanical gauges are dampened to stop them vibrating and jumping
around making them hard to read.
The ecu corrects this internally to provide a stable value for map value
selection but this will ALWAYS lead to an averaged value as you cannot
measure it accuartely no matter what ecu you have.