Standard pressure and temperature

[Lawrence C Leung]

The gauge is absolute, so the standard it compares things to is a vacuum.
Thus, no pressure at all (relative to a vacuum) is 0.0 bar. Atmospheric
pressure at sea level is 1.0 bar, which is the pressure of the
surrounding air, caused by the weight of the atmosphere above sea level.
2.0 bar means that the manifold is at 14.7 lbs/in/in (1.0 bar) ABOVE
normal atmospheric pressure. It's actually a fairly sizable amount of
pressure. 

Whether you can breathe a sufficient amount of oxygen at 0.5 bar, I don't
know. But, you could actually get that thin an atmosphere into your
lungs. You only couldn't do so if the air around you was at 0.0 bar.
Under a no boost condition, our car's often operate at 0.5 bar or so,
meaning that in the normally aspirated mode, our engines are breathing
rarified air. In NA cars, the pressure MUST be lower than atmospheric in
order to draw in air at all. The air becomes pressurized back over
atmospheric during the compression stroke, so the engine really doesn't
have to worry about running rich. 

LL - NY



On Tue, 20 Mar 2001 13:58:43 -0800 Huw Powell <audi at mediaone.net> writes:
>
>> >  This can make a big difference - at 100 degrees F and 10,000 
>feet
>> (altitude
>> >  of Leadville, CO, for instance), the density altitude is now 
>equivalent
>> to
>> >  about 15,000 feet, and the outside air pressure is only 15 inches 
>of
>> >  mercury, which means we need THREE bar showing on the boost gauge 
>to get
>> >  sea level air pressure (1 bar) plus .5 bar boost (total 1.5 bar) 
>in the
>> >  manifold and thus sea level performance.
>
>can you even *breathe* at 0.5 bar???
>
>and
>
>Isn't the gauge absolute?  doesn't it simply measure the pressure in 
>the
>manifold relative to a spring or some such?  It seems odd that it 
>would
>be calibrated so 1 bar on it is equal to "whatever is outside"...
>
>-- 
>Huw Powell
>
>http://www.humanspeakers.com/audi/
>
>http://www.humanthoughts.org/