Boost Pressure Log vs Tune

[LBZ]

Struggling to remember my tuning knowledge. Been awhile…….

So when logging my LB7 tune 5 in my DSP I’m only seeing 21psi (145kpa) on my gauge but 35psi (240kpa) in the log.
Atmospheric pressure is about 13psi (88kpa).
Tune max’s out at 37psi (255kpa).

So does the boost pressures in the tune include the atmosphere or is that before atmosphere? It would appear I’m seeing boost pressure + atmosphere in the log.

 

[2004LB7]

If I'm not mistaken, since its been awhile, there was two or more boost pids. One for PSIG and another for PSIA. I don't believe they where well labeled as to which one is which. With the V8 software you can set them to add or subtract your ambient pressure as desired in the pid settings

 

[LBZ]

Ya I still log in the old 7.5. I need to update myself I guess. There is only one boost pressure pid in there that works.

 

[LBZ]

My question more pertains to when the ecm reads boost pressure and references it to the boost table is it including the atmosphere in its readings or psig with the atmosphere pulled out of it already?

 

[2004LB7]

I think I remember calculating the table by subtracting the ambient pressure, then calculating the pressure ratio of the turbo for the various cells, then adding back the ambient pressure. That would make it PSIA. But I think the PID is PSIG or doesn't include atmospheric pressure

 

[PureHybrid]

Table is PSIA. The pressure in the log at idle speed will let you know if it's absolute or gauge

 

[darkness]

Seems to me I see both in my logs. I still use 7.5 as well. I’ll look at one when I get home.

 

[darkness]

The boost table includes atmospheric pressure. Here’s a pic of a log file. It reads boost and map pressure and atmospheric pressure.

 

[LBZ]

Kind of what I suspected. I’ll make some tuning changes and see how far I can go with it before the wastegate head cuts off the boost.