rsg1963

Some of you may be misunderstanding the OP question and may misunderstand physics for that matter, so I cut and pasted a simple explanation from the web below. Also to the point of the original question: The boost does not really increase or decrease due to elevation. It boosts with throttle demand. Inherently it's more efficient at altitude than a Naturally aspirated engine. Bottom line: Turbo's maintain power far better at altitude, period. Regardless of what engine you throw it on, V-8, V-6, Diesel, etc..
***A turbocharger compresses the air flowing into the engine. This way, more fuel can be burned, which results in greater power from each explosion within the cylinder. Experts estimate that normal atmospheric pressure at sea level is roughly 14.7 pounds per square inch (psi, which is the equivalent of roughly 1 bar) and that a turbocharger can compress the air by 6 to 8 psi (0.4 to 0.55 bar). This means that a turbocharger can pump roughly twice as much air into the engine. Since the system isn't 100 percent efficient, the engine will probably get a 30 to 40 percent boost in power, rather than a 50 percent boost. To be clear: That's 30-40% MORE than a Naturally Aspirated engine like the Coyote.

Kingofwylietx

Good point rsg1963, we got off topic.

To the OP, your answer is basically yes. The turbos are able to pressurize the air so you lose less power (by percent) than a naturally aspirated engine. See the link posted by Blown F-150.

RandyinTN

Why does Ford tell you when you are towing at altitudes above 1,000 feet to reduce the combined gross weight when towing by 2% for each 1,000 feet you go higher?

Blown F-150

I was told that it is due to the reduced cooling ability of the thinner air. It has to do more with the ability to keep the enigne cool than the ability to make power.

Kingofwylietx

That question isn't relevant to the OP question at all. Perhaps make a new thread for that question, surely someone knows the answer.
edit: Blown F-150 answered while I was typing. His answer makes perfect sense to me.

gone postal

Less density in the air going through the radiator/intercooler=less efficient heat transfer.

Blown F-150

Less dense = Thinner in layman's terms.

Eric Kleven

Turbo will spin faster to make the same manifold pressure at a higher altitude, the lower pressure the turbine is exhausting into raises the pressure ratio across the turbine (given the same driving pressure in the exhaust manifold), increasing the power produced by the turbine, and spinning the turbo faster. This is balanced by the compressor needing to absorb more power to create a higher pressure ratio in compressing lower pressure air to the same manifold pressure it wants at sea level.

There is a point where a turbo will run out of RPM and won't be able to produce the manifold pressure called of it, but I'm willing to bet that critical altitude is a helluva lot higher than any road you'll ever be on. No-boost 'turbo normalized' aircraft engines typically hit that wall at about 24,000' MSL. A boosted engine will hit that critical point at a lower altitude. (this is why the old WW2 turbocharged aircraft also had an engine-driven supercharger, 2 stages of boost were necessary to make the desired power levels at the desired altitudes.)

RandyinTN

I thought the turbo speed was controlled by the exhaust running through it?

Kingofwylietx

Eric Kleven alluded to the operational differential in pressure between the exhaust gasses at sea level vs at elevation. At sea level, the difference between the exhaust pressure between the engine and turbo....and the atmospheric pressure on the exhaust side....is a differential pressure. Differential pressure created by the exhaust spins the turbo.

You are looking at it too simply. Given the same pressure from engine to turbo, at a higher elevation the differential pressure across the turbo is greater because atmospheric pressure is lower. Engine exhaust pressure minus atmospheric pressure equals differential pressure. The higher differential pressure is why they can spin faster at higher elevations.

This doesn't account for the work being done by the turbo...that's another topic.