# how psi is measured when adding more



## 435iBlkMamba (Jan 29, 2014)

I was wondering how they raise the boost on turbo cars? Lets say its stock is 8 psi and I get the BMS stage 1 and they say an extra 3 psi. Does the tune in the box actually read it as 11 psi or does it just adjust for the extra psi not really knowing the actual total psi? 

Kinda hard to explain but lets say you have the stage 1 with 3 extra psi and then get the BMW performance tune, would it increase the psi another 2 or 3 psi over the stage 1?


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## milKt (Apr 26, 2014)

Tuning on turbo BMW cars is not PSI dependent.
The actual tune does not "READ" any PSI.

There are quite a few other variables:

a. the metered air (blow-thru MAF or draw-thru MAF used?)
b. injector size.
c. load
d. temperature
e. timing

The good "proven" base-tune will, however, generally adjust well to small changes in power, pressure, etc.
More often than not (with larger changes in turbo settings), the fuel pump or injectors may need to be upgraded to keep up with proper fueling.

Consider.


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