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Re: Turbos at Altitude (long)

> Road & Track had some useful material on this issue in consecutive issues
> in 1988.  April, p. 191 and May, p. 166.  Included is a graph from Porsche
> showing how the power of a conventional turbocharged engine, with
> differential pressure control, drops with altitude (at a rate of about
> 2%/1000 ft), and the 944 Turbo, which has absolute control, and maintains
> its sea level power to 6560 ft.  Also noted is that Ford and Pontiac use
> absolute boost control; no mention of Audi (this in 1988).

FWIW, I noticed that my '89 200q would still make 1.8 bar of boost at 7500'
during my trip from Albuquerque to Phoenix ... lots of power (which is good
since I was pulling a 2300-pound trailer) but that's my subjective opinion.
BTW, I do have a stiffer wastegate spring installed and the ECU fuel cutoff
bypassed, in case you're wondering...

However, I did seem to have an occasional problem: every so often -- and it
varied, for reasons I couldn't figure out -- my car would start to buck and
surge at 1.4-1.5 bar of boost ... it would even happen as low as 1.1 bar if
I'd been into the boost for a while.  At one quick stop to buy fireworks --
I know, I know, but I couldn't resist -- I didn't shut the engine off and I
heard a loud buzzing noise from the fuel pump.  It wasn't audible inside of
the car but it sounded a lot louder than any of those on my other cars from

My first guess was the quality of gas since it didn't happen with the gas I
had in the tank when I left Phoenix but seeing that I filled up three times
and it didn't go away, I'm now thinking it might be a fuel delivery problem
instead.  I'm pretty certain it wasn't detonation -- I put the windows down
and listened to the engine sounds very carefully -- and it didn't feel like
an ignition cut-out.  I'll have to look into this further but it's my guess
that I've got a fuel pump that just couldn't keep up with a sustained heavy
load on the engine.

Any comments/suggestions?

     _             _             
    / l       l o l  \       l o   Jeffrey Goggin
   /__l l l / l l l  l l l / l l   * * * * * * *
  /   l l_l \_l l l__/ l_l \_l l   AudiDudi@delphi.com