PSI to KPA Conversion

[Mad_Trbo]

First I am wondering is there anyway to change it so that the VE table reads in PSI instead of KPA along the vertical axis?

If not is there anyway to convert KPA to PSI, I have an excel sheet I use to make mass changes to my fuel table. I actually developed it for my AEM EMS and it looks at a certain load which has a certain AFR defined for that load. If the load does not match it tells me how much to increase or decrease fuel for that RPM position.

The challenge I am facing is when I look at -psi, how does this convert on KPA? I can log PSI off of XFI but when i go to make fuel changes, I need it back to KPA, but I can't seemt to make sense of the conversion.

 

[JCotton]

First I am wondering is there anyway to change it so that the VE table reads in PSI instead of KPA along the vertical axis?

If not is there anyway to convert KPA to PSI, I have an excel sheet I use to make mass changes to my fuel table. I actually developed it for my AEM EMS and it looks at a certain load which has a certain AFR defined for that load. If the load does not match it tells me how much to increase or decrease fuel for that RPM position.

The challenge I am facing is when I look at -psi, how does this convert on KPA? I can log PSI off of XFI but when i go to make fuel changes, I need it back to KPA, but I can't seemt to make sense of the conversion.

If you record, PSI and KPA at the same time, the psi number is whatever the KPA number is.... it's already converted in the recording... or am I missing something here...

 

[Mad_Trbo]

If you record, PSI and KPA at the same time, the psi number is whatever the KPA number is.... it's already converted in the recording... or am I missing something here...

Does that mean you don't know the answer either?

Just kidding, sometimes we can't see the forest for the trees, good point - thanks

 

[bobc455]

First of all I wouldn't listen to that Cotton Guy. He's still new at all this. (j/k)

As far as I know you can only look at KPA in the fueling tables. But once you do it for a short while, it is easy to get accustomed to thinking that way. 200 kPa is ~ 15 PSI. 100 kPa ~ 0 PSI. 0 kPa ~ -15 PSI. Once you keep playing with the tables for a little while, it will all become second nature.

The difference is that kPa is an "absolute" scale = 0 kPa is a perfect vacuum. Actually this is also true for PSI, since atmospheric pressure plus boost gives manifold pressure; if you are running 10 PSI boost, your "true" PSI is ~25:
15 PSI (atmospheric pressure) + 10 PSI (boost) = 25 "absolute" PSI. When people are talking about "boost", the atmospheric pressure is roughly fixed, so the "boost" is the only thing worth discussing...

-Bob Cunningham

 

[Mad_Trbo]

First of all I wouldn't listen to that Cotton Guy. He's still new at all this. (j/k)

As far as I know you can only look at KPA in the fueling tables. But once you do it for a short while, it is easy to get accustomed to thinking that way. 200 kPa is ~ 15 PSI. 100 kPa ~ 0 PSI. 0 kPa ~ -15 PSI. Once you keep playing with the tables for a little while, it will all become second nature.

The difference is that kPa is an "absolute" scale = 0 kPa is a perfect vacuum. Actually this is also true for PSI, since atmospheric pressure plus boost gives manifold pressure; if you are running 10 PSI boost, your "true" PSI is ~25:
15 PSI (atmospheric pressure) + 10 PSI (boost) = 25 "absolute" PSI. When people are talking about "boost", the atmospheric pressure is roughly fixed, so the "boost" is the only thing worth discussing...

-Bob Cunningham

Thanks for the break down, I hate that I grew up on PSI and A/F. It appears he better tuning tools are Lambda and KPA. Your simplified explanation helps.

Just so I am clear 100KPA = 15psi(atmospheric pressure), so you should be able to take a ratio. If you have 150KPA you should be able to take 50% of 15 psi and if you want to convert back to KPA you should be able to divide your PSI reading by the fixed atmospheric amount of 15 and come back to kpa for vacum, add 100.

And if you are in vacum you don't add the 100, good stuff.

 

[norbs]

One good thing about the dfi gen 6 and gen 7 is they both use psi for everything.

 

[oldtimer]

First I am wondering is there anyway to change it so that the VE table reads in PSI instead of KPA along the vertical axis?

If not is there anyway to convert KPA to PSI, I have an excel sheet I use to make mass changes to my fuel table. I actually developed it for my AEM EMS and it looks at a certain load which has a certain AFR defined for that load. If the load does not match it tells me how much to increase or decrease fuel for that RPM position.

The challenge I am facing is when I look at -psi, how does this convert on KPA? I can log PSI off of XFI but when i go to make fuel changes, I need it back to KPA, but I can't seemt to make sense of the conversion.

How's this:

kPa -- PSI

314 -- 30.8
295 -- 28.1
275 -- 25.2
256 -- 22.4
236 -- 19.5
216 -- 16.6
197 -- 13.9
177 -- 11.0
158 -- 8.2
138 -- 5.3

 

[Mad_Trbo]

How's this:

kPa -- PSI

314 -- 30.8
295 -- 28.1
275 -- 25.2
256 -- 22.4
236 -- 19.5
216 -- 16.6
197 -- 13.9
177 -- 11.0
158 -- 8.2
138 -- 5.3

Good like gold, thanks!

 

[TurboTR]

But beware, the table given there implies MAP on one side and boost (gauge pressure) on the other. 138 kPa is NOT = 5.3 psi...

FWIW, kPa is not inherently an absolute scale. It's just another pressure measurement unit. The "MAP" aspect attached to the Y axis of the table(s) is what implies the absolute scale. Our engine controller cares about MAP. Some ecu sw erroneously displays a MAP label on a gauge pressure scale (or vice versa), which can be confusing.

TurboTR

 

[tuner]

Hey Norbs, yer buddy Anders (Club Corvette Sweden) is lookin' for you at:

http://www.innovatemotorsports.com/forums/showthread.php?t=1601

Pounds/sq. inch X 6.89476 = Kilopascals

Kilopascals X .14503 = lbs./sq.in.