Notice it's with altitude calculated in. You sure are smart. It's like saying 1 foot = 12 inches.Originally Posted by rewindspline
i.e. 1 BAR = 13.034 PSI at 3500 FT Above Sea Level
Originally Posted by rewindspline
Even without the altitude correction factor there seems to be confusion or at least inaccuracy. You might not care about the accuracy, but to set the record straight 1 bar does not equal 14.7 psi, it equals 14.5 psi.
You may have gotten confused since atmospheric pressure (1 atm) is 14.7 psi (14.696 psi to be more exact); 100kPa is also 14.5 psi.
1.41 BAR = 20.45 PSI at 0 FT Above Sea Level
i guess there's still a bit more boost in the stock twins, gonna go raise it to 1.6 and try them out! i seriously want the twins to just blow into a million pieces.. going single next week! w00t!
So you're saying boost gauges displaying in bar are essentially worthless at altitude? I don't buy it. I would suspect the gauges are calibrated to display 1.0 bar at 14.5 pounds/in^2 of pressure.
For the record, a bar is a bar and is equal to PSI regardless of elevation.
A bar is CLOSE to but not exactly 1 atm, and atm is the unit of pressure that changes.
Also, any good pressure gauge has a tap for a reference pressure measurement, that ought to auto-correct for any such elevation issue.
On another note: Have you guys played around with pressure ratios? I always thought those calculations were cool, especially considering it calculates the pressure in bar. Really, who needs a calculator?
Pressure Ratio = (14.7 + Boost)/14.7
Example 1 (for 12psi of boost): PR = (14.7+12)/14.7 = 1.82
In this example, approximately 82% more air will go into the engine than the engine could have consumed by itself.
Example 2 (for 38psi of boost): PR = (14.7+38)/14.7 = 3.59
Here approximately 259% more air will be going through the system.
The above pressure ratios are in Bar. Example 1 had 1.82Bar and Example 2 had 3.59Bar. Lets say your boost gauge is telling you that you are hitting 2.77 bar. This means that your car is consuming 177% more air than it could without the turbo.
I hope all this information helped clear the understanding of those who thought that 1Bar=14.5psi.........
Last edited by BadTdabone; 08-02-2011 at 08:41 PM.
I think I read here that you have a Master of Science degree pending? I hesitate to ask "what school" since it may just be an honest mistake on your part. So I'll chalk your erroneous comment up to simple lack of knowledge on something that is very simple and basic science, and you probably just forgot it since you don't work with pressure units. Btw, I am a mechanical engineer with a BSME and 40 years experience working with pressure vessels and I use bar and psi and other pressure units every single day.
Go find any science book that shows conversion factors, or any online unit conversion site...I like this one:
I like that fact that you mentioned pressure ratio since it's a very important parameter in turbo sizing. It's the absolute outlet pressure divided by the absolute inlet pressure. To convert gauge pressure to absolute pressure you add the atmospheric pressure at the specific altitude you are at; 14.7 psia is the correct atmospheric pressure at sea level.
Nick 95 6sp
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Last edited by BadTdabone; 08-03-2011 at 01:46 AM. Reason: Grammar Correction
I didn't "search" to find out about your MS, I saw you post that comment a while ago and simply remembered.
Thanks for posting the erroneous source for your comment. Now I understand why you thought you were right. This is another example of "be careful what you believe" and the importance of confirming information by checking multiple reliable sources. The bar = 14.7psi (vs 14.5) is a very common misconception and not much of an error in most cases, but it's wrong nontheless.
As far as engineers resorting to calculators, you must not know what an engineer is. A calculator is useless unless you know what to calculate. An engineer knows what physical parameters are involved and how to use them to solve the problem. A calculator just cranks the numbers faster than most humans can do it.
I garuntee you hardly do any full on calculus or differential equations on paper anymore. You just use programs to do it for you. You simply stick the data in the right boxes. Don't talk to me like I don't know what an engineer does. My father IS one!
Last edited by BadTdabone; 08-03-2011 at 02:43 PM.
data? what data? what boxes?
In any case, anyone looking to convert pressure units should just use the conversion site link posted above and you'll get the right answer.
Pounds per square inch
(psi, PSI, lb/in2, lb/sq in) Normal atmospheric pressure is 14.7 psi, which means that a column of air one square inch in area rising from the Earth's atmosphere to space weighs 14.7 pounds.
(atm) Normal atmospheric pressure is defined as 1 atmosphere. 1 atm = 14.6956 psi = 760 torr.
(bar) The bar nearly identical to the atmosphere unit. One bar = 750.062 torr = 0.9869 atm = 100,000 Pa.
Since 1 Bar is 0.9869 atm, then I now agree with you that 1 bar is 14.5psi. This is because 14.7psi x 0.9869 = 14.5psi The writer of the source I read must've been considering 1 bar = 1atm, which is close, but not accurate.
It's hard to to believe that a numerical value is wrong, especially when it comes from a very valid source that has been printed and published. I assumed it was right, because it was published. Not only that, but the equations seemed legitimate as well. I will have to email the publishers of the text and notify them of this error. Thank you for sticking in with the argument, but don't continue to test my backround and or persona, because I have an endless sea of engineer jokes to put out. Heheh.
I'm glad we now agree and can now move on to more important things, like engineer jokes.
Btw, since I've been an engineer since 1972, I think I've heard almost all engineer jokes. So if you know any new ones, post em up here and there ...probably not "correct forum manners" to do that in this thread. Feel free to throw them into your own threads or any of mine.
PS: good luck with your MS