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Fw: Audis at altitude

I moved to Boulder from Palo Alto two years ago and I paid dearly for it, in
the form of lost horsepower for the 4000 csq. I gained about 2 miles to the
gallon (not to mention lower octane less expensive gas) up to 27 from
approx.. 25. What I got for this nominal mileage increase is the privilege
to drive around at 80% of the power I had before. Not exactly a stellar
trade off given the q's not so great bhp/weight ratio. I knew one of the
opportunity costs of living at a higher elevation would be bhp, but I didn't
know just how much until I saw the SAE correction figures for horsepower at
5500 feet. The offset is that skiing up in Vail was great last week-end.

That means I'm cruising around at 85 bhp in the 4000, and my V8 jeep is
putting out 175 bhp. LAME! Driving up to the mountains results in even
greater power loss. LAME, LAME! So I've since decided that every car from
here on out will be force fed, hence the addition of the S4 to my stable.
Now if only Porsche would do a Turbo Boxster. Failing that I think I saw a
supercharged one in last month's EC.

-----Original Message-----

>I have lived at high altitudes for more than 20 years and have been
>continually impressed by how well the turbo cars do relative to the
>aspirated ones.  I am far from an expert on the subject and I guess it
>depends on how the turbo car measures and controls the intake pressure
>(boost).  If the boost pressure is absolute (say, 0.5 bar) then it is
>obvious that the turbo car loses a smaller percentage of it's intake charge
>than the normally aspirated car as the ambient pressure decreases  i.e.
>* .8 is 80% whereas (1.0 * .8) + .5 is 1.3, greater than 80% of the
>1.5 (where 1.0 is sea level pressure, .8 is the altitude multiplier and .5
>is the boost add) .  Any better informed listers want to comment?  All I
>know for sure is that turbos still pull hard at 11,000 feet when even the
>high performance normally aspirated cars start to wheeze.
>BTW, the downside is that turbo lag is accentuated by higher altitudes.
>Ralph Poplawsky
>'91 200Q
>'95 Volvo 850 turbo