[urq] Turbocharging & Elevations

[Buchholz, Steven]

... there is no argument that the turbocharger helps make up the
difference in the air density ... but it cannot do so completely ... the
difference in inlet air density means that the turbo has to work
"harder" to achieve a given manifold pressure ... which usually mans
that the charge temperature is higher at that pressure ... this is what
causes the differences between performance at sea level and altitude.
I'm not familiar with the SAE calibration method ... perhaps it
accommodates some or most of this effect ... 

... by the way ... there are different methods for measuring pressure,
some are relative and some are indeed absolute.  The boost gauge on an
urq is providing an absolute measurement ... i.e. it is independent of
the altitude at which the vehicle is operating ... 

Steve B
San Jose, CA (USA)
> 
> Turbocharging was developed on aircraft engines to
> give the plane the same performance at sea level as at
> high elevations.
> 
> Pressure is relative. The pressure is measured
> relative to the atmospheric pressure. If you fly at a
> low elevation you still measure 30 psi relative to AP.
>  If you fly at a high elevation you still measure 30
> psi relative to AP. Now the whole air density issue
> makes it a bit more complicated but in theory the
> turbo boosts more air to make up for the lower
> density.