Re: 91 200'isms

[Albert Ng <ang@copper.ucs.indiana.edu>]

Just my little something about this topic. I heard from somewhere a while 
ago that all the Audi 5kt car has a altitude sensor. If the car is operating 
at a certain altitude, the sensor will kick on and send signal to somewhere 
to fully open the wastegate. I don't know why they doing this, but, by my
guess, is that they want to keep the turbo spin slower since on a higher 
altitude the air density is lessen and the turbo will spin fast.  


Albert Ng
'87 5kcst

> Imagine going toward the other extreme.  Imagine going up a "mountain" until
> you reach a total vacuum.  There is no air present, therefore, no air to
> compress with your turbo compressor.  The ambient pressure would be zero and
> your manifold pressure would also be zero.  Granted, this extreme is not
> attainable on the surface of Earth, but the trend should be obvious.
> 
> Maximum manifold pressure will decrease with decreasing ambient pressure.  
> The effect of a wastegate is ignored here.  It will have an effect only at
> higher pressures, not toward the low pressure end.
> 
> At 04:13 PM 3/15/96 -0800, you wrote:
> >On Mar 15,  3:23pm, Eliot Lim wrote:
> >> Subject: Re: 91 200'isms
> >>
> >> On 15 Mar 1996, Joe Yakubik wrote:
> >>
> >> > hits 1.7 bar on a daily basis @ 2000 ft altitude; 1.8 bar nearer to sea
> >level
> >>
> >> perhaps this has been a long time misconception of mine, but i always
> >> thought that turbos would produce the same manifold intake pressure
> >				        ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> regardless of altitude..
> >
> >	This would be true (if *I* understand it correctly, of course!)
> >	if your compressor had enough capacity.  I believe this is usually
> >	*not* the case: manifold pressure may be wastegate limited at
> >	sea-level, but get into the mountains, and the turbo running full-tilt
> >	will still not trigger the wastegate.
> >
> >	Presumably (as mentioned in a previous thread), making a turbo
> >	larger would give it enough excess capacity to maintain maximum
> >	boost at any altitude, but that would result in ridiculous turbo lag
> >	times.
> >
> >	-Arun
> >
> >
> >
> >Arun Rao
> >Scientist
> >Pixar
> >1001 W. Cutting Blvd.
> >Pt. Richmond, CA 94804
> >(510)215-3526
> >
> >
> 
> ___
> 	Bob 
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>