Originally Posted by
ShelGame
The resolution issue is related to the limitations of an 8-bit computer. The MAP signal is digitized into 8-bits. That gives 256 'steps' for each 5v signal. So, if you have a 2-bar MAP, that is 29.4psi (total) divided into 256 steps, gives 0.115psi per step. This is the smallest increment of MAP change the computer can 'see'.
With a 3-bar MAP, that smallest step is larger. 44.1psi / 256 = 0.172psi per step. The concern is really in vacuum, not boost. This change in step size (or resolution), means that small vacuum changes can be missed resulting in fueling errors and drive-ability problems. Which can be made worse by 'big' cams and porting work. That can usually be 'fixed' by small adjustments in the O2 feedback values.
EDIT: Copied this post to the Turbonator Tuning Wiki