As you point out, the more compression the higher the temperature rise.
..The turbo is called upon to compress the air *more* as altitude goes up
(and temperature goes down). Since the compressor efficiency of a
turbocharger is less than 100% (actually about 70%), the air in the intake
manifold is hotter then higher you go at any given manifold pressure. When
I had a Turbo Lance with an aftermarket intercooler, there was a gauge that
measured temperature before and after the intercooler and could give the
difference as well. It was pretty apparent that all temperatures
(CHT/TIT/intake before intercooler/intake post intercooler) went up with
altitude if power was held constant.

Mike
MU-2

"Greg Copeland" wrote in message
news
On Tue, 04 Oct 2005 15:44:16 +0000, Mike Rapoport wrote:

The heating of the intake and the consequent reduction in density is the
reason that I think it will take more MP to produce the same HP at higher
altitudes with a turbocharged engine. At the same MP/RPM a tubocharged
engine is effectively running at a higher density altitude than a
normally
aspirated one. The turbocharged engine is also running at a higher
density
altitude as altitude increases at the same PM becasue there is more
compression required, therefore more heating. The intake air is heated
*substantially* and its density is reduced substantially. Natually, the
effect is strongest at high manifold pressures and high altitudes. I
agree
that reduced pressure at the exhaust helps and an intercooler certainly
helps too.

Just tossing this out there...

The final rise in temp is always relative to the ambient air temp. At
altitude, where temps can be quiet cool, you are getting a modest
"intercooler" effect. Additionally, amount of boost provided by the turbo
dramatically effects the temp delta.

As an example, a turbo pushing 10 psi, with no intercooler, may cause a
temp delta of 100' F (real world number), measured at the intake. If you
are at altitude, where ambient is quiet cold, say, 40-50' F., then the
intake temp, given the same boost, may only be 140-150'. Compare this to
take off, at sealevel, on a 95' F day, the intake charge may measure ~200'
F, given the same boost.

Turbonormalized is a little bit different because the boost is going to be
much lower at take off than at altitude...nonetheless, you are still
getting an intercooler-like effect from the cooler ambient air.

Greg