Guage Pressure Tuning

Good Evening,

I have been tuning using MAP as my load axis so I am familiar with 0-100 kpa for NA and 0-200 kpa for a turbo application with 15 psi of positive boost.

My question is if I wanted to start using guage pressure or MGP on my load axis how do the numbers cross over? I understand that with guage pressure on a NA vehicle 0 is equivalent to atmospheric or 100 kpa and that any positive numbers over 0 indicate positive boost. Where I am fuzzy is the cross over of the lower load numbers where on MGP or Guage pressure it drops into negative values. Is -50 equivalent to let's say 50kpa or -100 being equivalent to 0 kpa on the absolute scale?

Best,

Tom

MGP is simply the difference between the manifold pressure and the barometric air pressure. Let's say that the baro pressure measures 100 kpa and there is 50 kpa in the manifold. The difference of course is 50 - 100 = -50 kPa. Some ECUs use an onboard or external baro sensor as part of this equation while others will assume a fixed baro pressure.