I'm trying to figure out what's going on here....

I have the PowerFC with the Datalogit and I'm looking at a log for a run.

I see the "Boost" go up and down during my run with minimums at -625 and maximums at +100 or so. Hmm.

"PIM" voltage goes from around 1 Volt minimum to 4.7 Volts maximum. Looking at the service manual that is from basically 0 absolute pressure (or -1 bar) to about +14.7 (+1 bar) or so. This range is correct according to my mechanical boost gauge. I have the boost set at about 1 bar.

So. The question is... what the heck is up with "Boost". I see that it moves up and down with the PIM voltage, but it's almost like the top and bottom parts of the pressure value axis are compressed?

Why does "Boost" show -400 at idle (presumably in mm Hg; in agreement with my mechanical gauge) and only a measly +100 under full throttle at 14.7 PSI?

I don't get it.

Regards,
Brian

 

100 meaning 1.00, 1 bar? Where's the decimal point?

 

Becoming more frequent, many aftermarket manuals(including the DATALOGIT) are written with gross pressure conversion errors due to ignorant company personel!

The PFC manual states that the pressure values per P row are in absolute Kg/Ccm^2. Absolute pressure in PSI - 14.7 = relative pressure, or what your boost gauge displays. 1 kg/ccm^2 = 14.2psi.

The datalogit manual in section N-3 states "pressure value in the Fuel & IGN map is Bar(kg/ccm^2). That is a oxymoron. 1 ATM = 14.7 psi. ATM and Kg/Ccm^2 are completely different ways of measuring pressure.

Back when I ran pressure comparison values of my Autometer boost gauge to the PIM voltage on the PFC and PFC pressure displayed; it showed as pressure increased, the PFC displayed pressure became lower and lower in comparison to the Autometer. At 10psi, the PFC after conversion showed 9.5 psi. By 14.3 psi, the PFC showed 13 psi.

If you convert the P rows to their relative pessures, you would think that by 13.8psi you should be in the middle of P18. The PFC will show that. The datalogit will show 17. A friend with a single turbo and datalogit said it looks like the PFC will never ever hit row P19 and most likely not even P18 due to pressure conversion errors.

Many other PFC owners have also noticed this discrepancy.

When showing 12PSI boost on the Autometer, the datalogit showed a consistant boost of 75.
Converting and rounding to the nearest 10th:

.75 ATM = 11.0psi
.75 BAR = 10.8psi
.75 Kg/ccm^2 = 10.7psi.

What the *** is it?

 

While you are on the subject of pressure discrepancy,
Which of the following is most accurate:
Autometer mech Boost (doubtful)
Blitz dual turbo timer with digital boost readout
PFC boost monitor...?
I have noticed a rather large .07 kg/cm^2 difference between the blitz and PFC
PFC will give me .65 and I will get .72 on the blitz...
Which one should I follow ?

 

I am waiting for my replacement Blitz Dual SBC to arrive. The first one was defective, it would turn off at .08khPa or about 1 PSI. Then I'll compare it's reading to the PFC and Autometer.

This has ben discussed previously on this forum. Search for it. Use nanometer!

 

Maybe it depends on where pressure is being read from. I've always noticed a discrepancy between what my AVC-R reads and what the PFC displays.

 

At idle my PFC reads -400 mm/Hg and my Autometer reads -13.5 in/Hg. That's off by about -2.2 in/Hg.

At max boost my Autometer reads 15 PSI and my Commander says 0.89 kg/cm ^2. That's off by about 2.35 PSI.

I always assumed my Autometer was reaching the end of it's useful lifespan, but could it really be right and the PFC wrong? Or is the true correct number somewhere inbetween?

 

Check out his thread: https://www.rx7club.com/forum/showth...&highlight=pim