I've gotten about 10 pm's in the last month with peeps asking the purpose of the 3 Bar MAP sensors on the LNF if you use a stock base file for the tune.
The short answer is "Because!" This is an FYI so feel free to add your input as you see fit.
First of all the stock sensors are 2.5 bar. 2.5 bar absolute is ~36.26 psi, now subtract 14.7 psi for 1 atmosphere and you are left with the ability to read and control boost up to ~21.56 psi.
3 Bar MAPs following the same example would be ~43.51 psi, subtract 1 ATM and you can measure and control to 28.81 psi boost.
I understand the ECU limitation for logging the manifold pressure is 255 kPa, or 2.55 Bar, this appears to be the same for the 2.5 or 3 bar sensors. We are left with this limitation in logging the mani boost.
The Lower Charge Pipe MAP is another story however. It is listed in the PID's as Boost Sensor LoRes (PID.2338.PSI) and appears to be capable of 512 kPa from what I have read. This gives us the ability to log and control boost pressure up to the limit of the sensor or ~28.81 psi boost.
While you can certainly boost over the 21.56 psi fooling the ECU with the stock sensors, it runs out of the control area, in other words, you are just telling it to shoot for the moon with no means of really controlling it.
The benefit of using the 3 Bar MAPs is expanding the control range.
The purpose of pasting the data into the stock base file for the 3 Bar MAPs is that there seems to be less turbo overspeed control in the stock file than the GMS1 base file. I have no formal proof, but I can tell you the same tune holds more boost and much longer with the stock file than the GMS1 file. Remember there are many, many ECU tables we have no access to.
The 3 Bar sensor data that needs to be pasted into the stock file is shown below once more. You have to expand the precision of the fields out as far as you can to make it accurate.
Right click on the field Title box, select Precision and expand it to all the digits.
Here's the 3 Bar data...
At WOT the mani pressure is essentially equal to the lower boost pressure minus the TB pressure differential so we have the ability to log boost up to ~28.81 psi using the Boost Sensor LoRes PID.
The formula I use is =[PID.2338.PSI]-[PID.51.PSI] in the scanner table and chart. PID.51 is the Barometric Pressure (SAE) PID. Subtracting the atmospheric pressure from the Lower CP pressure lets you see the level of boost above atm. You will see 2-3 psi pressure in the lower CP during cruise speeds as the turbo is building some boost even though the manifold is in vacuum with the throttle plate only partially open.
I hope this helps explain why the 3 Bar MAPs are preferred. It is always better to tune a system within the control range rather than to let it run 'Out of Control'.
Now that CED offers pigtail adapters for the 3 Bar MAPs, they can be installed plug & play.