Re: Turbos at Altitude

[Larry Augsburger <71564.2244@compuserve.com>]

>  As far as I can tell, our cars control it relative to atmospheric
> pressure.  For instance, a stock '89-'90 200TQ allows 0.4 bar above
> atmospheric (or 0.8 in the case of mine with modified wastegate spring,
> etc.).  Thus at whether you're at sea level or 7,000 feet, when you first
> turn on the ignition, the boost gauge will read 1.0; at full boost it will
> read 1.4, but at 7,000 feet, atmospheric pressure is actually  0.77 bar, so
> you're really operating at 1.17 bar.

 I don't thinks thats right. Pressure is pressure. The car
controls boost pressure according to absolute pressure. The
wastegate doesn't compensate somehow for lower initial intake
air pressure. The pressure, regardless of altitude, will be 1.4
at full boost. However, the turbo will have to work harder to
get there because the air must be compressed more than it 
would at lower altitudes.I believe an engine at higher altitudes
would have the same power output as at a lower altitude, at the
expense of increased turbo lag time. This is not the case, of
course, with NA engines.

Brett Augsburger