Trevor

I romped on it on the way to work this morn. Boost showed a peak of 0.69 kg/cm2 (9.81 psi). My gauge showed a little over 11 psi. I live at 3075' altitude where ambient pressure is approximately 13.13 psi (compared to 14.70 psi at sea level).

If it reads absolute then I'm in there. If it doesn't I bet I have a leak in my MAP sensor vaccum connection.

cewrx7r1

iTrader: (2)

The PFC manual tells you exactly what it is, and many threads also mentioned that as boost increases the PFC reads lower and lower than true boost pressure.

Trevor

I've read the manual many times. Page 13 of the FC Commander manual says that Display Mode Boost is "Intake Manifold Boost Pressure". It makes no distinction if the reading is absolute or gauge pressure.

Living in Houston at 46' above sea level you probably wouldn't notice any discrepancies between the two boost readings if the Power FC does show absolute pressure.

Trevor

It's absolute. One guy went from 659' to 7250' and watched his PFC boost readings drop thru the floor while the gauge readings stayed the same.

cewrx7r1

iTrader: (2)

The PFC reads the PIM voltage which is then converted to ABS (see page 20 bottom right enclosed block), than converts to the KgCcm^2 value.

See it says ABS. Even so at near sea level, the calculations are off. And as boost increases, the boost reading gets progressively lower than gauge pressure.

cewrx7r1

iTrader: (2)

Should say bottom left!

Silver7even

Yes the PFC dose read in absolute pressure. If you live above sea level, as I do at 6000ft, then your relative boost gauge will indicate a lower absolute psia than it would at sea level, in my case 14.7-11.8=2.9 psi difference. So when I read 16 psi on my relative boost gauge, the absolute is 27.8 psia vs. at sea level read reading of 16 psi on a relative gauge, which would correspond to 30.7psia. Target AFRs are valid at higher altitudes. When reading a manual relative boost gauge you can subtract the altitude correction to make comparisons to people at sea level.

Feet below/above sea level
Vs.
psia lbs. per sq. inch absolute

-5,000 17.48
-4,500 17.19
-4,000 16.9
-3,500 16.62
-3,000 16.34
-2,500 16.06
-2,000 15.78
-1,500 15.51
-1,000 15.23
-500 14.96
Sea level 14.696
500 14.43
1,000 14.16
1,500 13.91
2,000 13.66
2,500 13.41
3,000 13.17
3,500 12.93
4,000 12.69
4,500 12.46
5,000 12.23
6,000 11.78
7,000 11.34
8,000 10.91
9,000 10.5
10,000 10.1