Quote:
Originally Posted by midnite_wrex
air pressure at 5000ft altitude is 2.4 psi lower than sea level. so his 15 psi is about 17 and a half at sea level.
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Its more than that......im at 2700 feet and my logged boost target is offset 2 psi from the map values....and im exactly 1 psi lower.
Heres the equations for an 06 STi
Atmoshperic Boost Compensation -> calculated as follows:
multiplier = (logged atmospheric pressure * .05208) + 0.25
multiplier is limited to between 0 and 1.
target boost absolute = target boost map value + 14.7
target boost psi relative sea level with atmospheric comp = (target boost absolute * multiplier) - 14.7
Multiplier = (12.3*0.05208)+0.25 = 0.8905
Target Boost ABS = 19psi + 14.7 = 33.7 <---- i figured out the 19 in excel. basically what boost target is needed in the map to achieve a final boost target of 15 psi
Target Boost PSI relative sea level = (19 * 0.8905) - 14.7 = 15.3 psi
Basically however much your ATM Pressure is lower than 14.7 your final boost target will be 2x that lower.
IE 13.7 atm pressure will yield boost targets that are 2 psi lower than map vales
12.7 ----> 4 psi
11.7 ----> 6 psi
Its not simply "you're 1 psi low so you're reduced 1 psi".......its double to offset the compressors lower efficiency.