How do you convert the boost level on the pfc which is mmHG to lbs/square inch? My PFC reads +.69mmHG, so how do I convert that to see how much boost I have my turbo set at?
Thanks,

 

Search the web as there are many conversion programs available.

Or do the math by hand.

 

I searched for conversion tables and didn't find one with mmHG

 

Windows:
http://members.execulink.com/~pjones/

PalmOS:

http://www.pe.net/firm/dpw-designs/p...it/cvt_it.html

 

http://www.onlineconversion.com/pressure.htm

Doesn't have mmHg, but has cmHg. Just multiply your result by 10.

You sure about your terminology though? Vacuum is described in terms of mmHg or inHg. I think you want boost, which is described in terms of kg/cm^2 or psi.

 

the pfc gives a boost reading in mmHG format. If it was vacumm, why does it say boost? one of you guys is bound to have done the conversion before

 

vacuum | boost
<------0------->
mmHg &nbsp;&nbsp;| kg/cm^2


Damn I hate doing ASCII art here...

 

so then I should be able to convert the kg/cm^2 to psi correct? Thanks

 

For the conversion challenged:

First there is two basic measurement concepts.
1. absolute which includes the pressure of the earth's
atmosphere.
2. relative which is pressure above that on the surface of the earth.

1 atmosphere (AT) = 14.7psi standard at sea level
1 BAR = 14.5psi
1 Kg/CcmSq = 14.2psi

Boost gauges normally display realtive pressure.
When my gauge reads 12psi boost, that is relative pressure. In absolute it is 26.7psi.

If you look at the pressure values in the PFC for the map rows, it is in an absolute derivative. See the bottom left of page 20 of the PFC manual.

 

I am lost. How much boost would .86 on the PFC be in lbs. via a boost gauge? I knew that 1 bar was 14.5psi but I also heard that .90 is 13lbs. How does this formula work? I have never had my car past .86 on the PFC and sometimes when it is hot I will only get up to .79 on the PFC. I thought I was running at around 13lbs of boost but I may not be. My mods are listed below. Thanks

 

The measurement on the PFC is Kg/cm^2 (boost). Chuck listed the conversion above.

 

psi = kg/cm^2 * 14.22

So, you see 0.86 on the Commander: 12.23 = 0.86 * 14.22
You're hitting a little over 12 psi.

Now, don't expect to see this on your boost gauge. Why? Because that would be way too easy. This topic has been debated on this forum several times... some have suggested that it has to do with your location above sea level, others have suggested that it has to do with the MAP sensor.

Some people's boost gauges are close to what the PFC reads, other's- like mine- are pretty far off. I've seen 0.91 on the PFC and 1.1 on my Apexi boost gauge, a difference of 2.7 psi!

Which one should you trust? I agree with Chuck in that you should trust the boost gauge. It takes the boost reading from the same place on the manifold regardless of ECU. So if you saw 10 psi when you were stock, you should be able to trust it with the boost produced by the PFC.

-Scott

 

so, my pfc was reading .69 which when put into the conversion table to convert from kgf/cm^2 to psi came out to about 9.8 lbs. Is kgf/cm^2 the same as kg/cm^2, because that is all the conversion table offered? I am assuming this is correct. That is not what my boost gauge says though. You say to go by the boost gauge? How is yours hooked up to ensure the line is leak free? I 'd hate to crank the boost up so that my boost gauge is accurate, but actually be running way to much boost.

 

how would it be that the pfc reading is incorrect? does that mean some of it's other readings may be incorrect as well?

 

Yeah, kgf is the same thing. All it stands for is kilograms of force.

You say you got 0.69 on the PFC, or 9.8 psi. What does your boost gauge show? I don't think I've ever seen anyone say that the PFC reading is higher than the boost gauge. But that doesn't mean it couldn't happen. Err on the side of safety: if your boost gauge reads higher than the PFC, tune by it. Worst case, your PFC is actually correct, and the result is too less boost, not too much.

My boost gauge is electronic, so there's only about 1 foot of vacuum hose between the manifold nipple and the boost sensor. I doubt there's a leak. Plus, as I stated above, my gauge always reads higher than the PFC. If I had a leak I would be getting low readings.

Didn't I give two reasons why the PFC could be incorrect in my post above? The PFC displayed values are only as good as the stock sensors. Take them for what they're worth, and if you don't like them, buy a bunch of gauges.

 

If you find my old post on this subject where I listed recorded values; you will see that I had two different boost gauges which read exactly the same boost pressure.

This pressure also matched the map sensor output voltage as detailed in the Mazda's manual. The voltage displayed by the PFC also matche the map sensor voltage.

WHAT WAS WRONG? The PFC converted the voltage to a pressure value that did not match the other three.
A conversion error!!!

 

Thanks for being patient with us Chuck. I remember you posting that info awhile back, but I was too much of a newbie to understand it.

For the new folks here, this is the post he was referring to: https://www.rx7club.com/forum/showth...threadid=36412

The cliff's notes version is that the PFC displays the MAP sensor voltage correctly (in the Etc. section) but screws things up when it converts this voltage to vacuum/boost. Moral of the story is trust your boost gauge.