lbs vs Bar (boost measurement)

Rodsrsr · Rodsrsr's Garage

Can someone help me understand how to convert boost measurements in bars to lbs. example 1 bar boost = how much in lbs?

jbrinkley · 07-12-2007, 06:22 PM

http://www.britishmetrics.com/html/pis-bar.htm

marlinaness · 07-12-2007, 06:23 PM

As I remember it, 14.3 psi per bar. I am sure google has plenty of converters.

Wil Ferch · 07:07 PM

Man ...be careful !!!

Normal atmospheric pressure at sea level is 14.7 psi or 14.7 pounds per square inch. We would call this 14.7 psia ( absolute). If this were a "gauge" reading, in comparison to atmospheric pressure..it would be "zero" psi ( or zero psig). The same "thing" can be zero or 14.7 if we speak absolute basis ( psia) or gauge basis ( psig).

14.7 psia = 0 psig
15.7 psia = 1 psig
16.7 psia = 2 psig ..... etc.

I bar ( gauge) = 14.5 psig.
2 bar ( gauge) = 29 psig....etc.

So.... a tire at 32 psi (or more correctly, 32 psig) would also be correct to say its at 46.7 psia.

Be careful what you're comparing.....best if they're both on the same basis ( gauge or absolute as you go from bar to psi).

- Wil

sww914 · 07-13-2007, 08:36 AM

I've always found it interesting that the air fuel ratio for most complete combustion is 14.7 to one, (lambda) the same number as 1 bar, 14.7psi, which is the air pressure at sea level.

TerryBPP · 07-13-2007, 08:48 AM

1 bar = 14.7 psi.

rick-l · 07-13-2007, 10:21 AM

In the google search window type in "1 bar in psi" (or "2 bar in psi" etc.).

GOOGLE

Porsche_monkey · 07-13-2007, 10:30 AM

Go to google and search for convert.exe, download and instal. That will solve all your conversion questions.

Wil Ferch · 07-13-2007, 11:42 AM

Jeez....

to TerryBPP..... NO ..... I bar is not 14.7 psi...it's 14.5 psi

Ohh... and not to lose the original nuance I posted...that would be 14.5 psig ( psi-gauge)...not psi absolute or psia.

- Wil

rootmatt · 07-13-2007, 05:38 PM

One bar is not quite equal to one atmosphere. According to google's calculator:
"1 atmosphere = 1.01325 bar"
That should explain the 14.5psi v 14.7psi.

But who am I to split hairs?

Wil Ferch · 07-13-2007, 06:51 PM

Yep..that DOES explain it......

It's more a question of answering questions correctly with facts instead of saying its splitting hairs. People are asking for conversion factors... no use giving them something that's wrong, and that wrong answer stays in these archives for later reposting or viewing by others.

- Wil

Rodsrsr · Rodsrsr's Garage

I think I got now. thanks for all the "detailed" answers.

TimT · 07-13-2007, 07:52 PM

jeez geeks.... lighten up.... you do realize your talking about a delta of something like .1455714025 to the nTH PSI difference?

and what is the resolution of the gauge?, how much dampening?what is the response time of the gauge?

oh BTW, I'm an engineer... I went to skool for a few yearz and learnt calc and phsiczs and thermo and stuff

I can sweat the details but this is ridiculous..

Call 1 bar 15 psi

rootmatt · 07-13-2007, 09:40 PM

But that's the way these threads go. Someone asks a perfectly reasonable question then folks like myself hijack the thread to discuss points of merely academic interest. As long as the question is actually answered, the rest is entertainment.

Cheers

Matt

Wil Ferch · 07:55 AM

Being correct or being incorrect is not simply an academic interest.

I'm surprised an engineer is saying small increments don't matter. I deal with high pressure pumps and if the spec says 72 bar, the difference is 14 psi ( 1044 psig vs 1058 psig)...so these "small numbers past decimals" ... *do* matter !!.

And the psia vs psig issue seems to be lost on everyone.. 14.7 psia = 0 psig. This can lead to a BIG misunderstanding if not properly understood. A tire with 32 psig can also be said to be at 46.7 psia. Same thing.

So...we need to know what we're talking about and to use the right terms. Even the original post is wrong in that "lbs" by itself means nothing in terms of "pressure". It's pounds per area ( square inch).

- Wil

WERK I · WERK I's Garage

Quote:

Originally posted by TimT
jeez geeks.... lighten up.... you do realize your talking about a delta of something like .1455714025 to the nTH PSI difference?

and what is the resolution of the gauge?, how much dampening?what is the response time of the gauge?

oh BTW, I'm an engineer... I went to skool for a few yearz and learnt calc and phsiczs and thermo and stuff

I can sweat the details but this is ridiculous..

Call 1 bar 15 psi

+1
Will, if you are sweating 14psi variance on an application that runs 1044psig, you have a very unstable product! We're not building Space Shuttle engines here!

jbrinkley · 07-14-2007, 05:32 AM

and fer christ sakes, no one has an absolute gauge in their car.
next thing you know some one is going to add altitude to the equation with a sealed gauge.

spuggy · 07-14-2007, 06:31 AM

Quote:

Originally posted by jbrinkley
and fer christ sakes, no one has an absolute gauge in their car.

Jim2 on the turbo forum is doing just that - running a gauge from a twin-engined bomber, and several other people like it so much after watching his video they're doing something similar...

If I'm not mistaken, the factory boost gauge on a 951 reads absolute pressure (they max around 2 bar indicated, and they don't run 30 PSI of boost).

Wil Ferch · 07:51 AM

Ya know...fuhgetaboutit...

Boost can be stated in inches of mercury, inches of water column...psia ...psig ....anything.

Go ahead..... mix 'em up ...sorry for introducing some accuracy in the discussion. As to the psia and psig difference...I wanted to illustrate that "way out" decimals have an affect on two digits in front of the decimal, if you get high enough. And yes...it may indeed make a difference. Have you worked with ASME code certified pressure vessels and exceeded design limits? I wouldn't want to go to court on that !

If you want to see where it really matters....mix up psia and psig in low pressure applications, like where 14 "psi" might be 28 because the wrong system was used....you know...off by "only" 100%.....

yeah , right.... "pounds of pressure".... gimme a break!

- Wil

equality72521 · 05:45 AM

You know Wil, I've followed your replies to numerous threads and you always go deeper than most people on the physics of the subject. Many find this to be going over the top and unnecessarily precise. I for one am glad you do. I would rather know the facts to the nth degree and then decide for myself how much error I am willing to live with. I do NOT want someone else's error factor; many say "good enough" and that may not be "good enough" for me. Please don't stop posting replies with this great FACTUAL information. I for one appreciate it. Newtonian mathematics can be said to be "good enough" but if Einstein didn't want to go deeper to explain the minute errors in the math we wouldn't have General Relativity. Maybe bringing Relativity into this is a little off topic but it explains my point. Keep up the good work.