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Discussion Starter #1
So if I were driving around Denver in my 1.8T, how much power would I be down from driving at around 1000 ft like here in PHX? Does the car automatically adjust to the altitude? It seems I remember a while back you would have to manually retard your timing or advance it or something. I know turbochargers make the elevation change less of an impact, but I'm sure it's still there.
 

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In theory none! But it depends on the size of your turbocharger, engine, how well its matched etc!! With a NA car, as you drive up the hill, the air density gets lower, therefore at wide open throttle you are operation at 14.0 psi absolute pressure rather than the 14.7 you got at 0 feet. (its actually all less than that, but you get the idea). As you drive up a big hill with your turbocharged car and increase in altitude, the ECU will still ask for the same amount of intake manifold boost (10 psi, 15psi or whatever your chip wants) at wide open throttle (controlled by your wastegate) and if the turbocharger is big enough, the turbocharger will simply operate at a higher pressure ratio (Poutlet/Pinlet) and therefore a higher turbo speed to create that same amount of boost-therefore the same amount of power (unless the B5 has a derate for altitude, which I doubt because I don't remember hearing about any ambient pressure sensors). It will typically have enough energy on the turbine side to spin rotating assembly at the higher rpm because the turbine out pressure is lower, and therefore the expansion ratio on the turbine is slightly higher. What stops you from driving into outer space at full power is the turbocharger speed, (typically a limit of blade tip speed.) Also, you will start running lower compressor efficiencies once you get out of the "meat" of the map and start running really high pressure ratios (current passenger car turbos typically max out at 3:1), so your intake manifold temperature will increase and power will decrease.
In summary, its a case by case basis, but at 5000 ft, I'd assume that a stock 1.8t is still putting out stock power, while a GIAC chipped 1.8t may be putting out closer to neuspeed power. -5hp? The best way to know would be to go get your car dynoed in Denver and then Pheonix.
 

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On a K03, especially with some ECU mods, I would expect you to lose a pretty significant amount of power because you're pushing it's flow capabilities even at sea-level. If you have a larger turbocharger and are octane limited at sea-level, it should compensate for the thinner atmosphere a great deal in terms of absolute horsepower but it will cost you in the form of a much higher boost threshold.
 

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Discussion Starter #5
I wonder what the air density difference is between 1000ft at 110F verses 5500Ft and 85F? What I loose in elevation may be partially mitigated by the cooler tempeatures.
 

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i have this little prog that calculates the air density at work. don't know if it does elevation, but it does do temp. i'll try to check it out tomorrow.
 

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I could always tell a difference in the 1.8T going from here (Denver) to sea level. Much more power - it was like getting chipped again. :D

My dad who is an aircraft engineer/inspector/mechanic was saying that turboprop planes would crap out at about 10k ft, whereas a supercharged engine could keep on going without losing performance.

I know my B5 didn't like breathing that thin air up at 14k' on Pike's Peak or Mt. Evans!

(side note: typically you lose about 3 degrees F in temp per 1000 ft.)
 

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The B5 does have an ambient pressure sensor located in the ECU box. I think the ECU uses it to anticipate fuel trims off boost. The main thing you'll notice is the increased lag but your peak hp will be the same. The elevation that a turbocharged engine begins to lose hp (when the wastegate is fully closed, ie it can't make any more boost) is called it's critical altitude). I'd say the K03 starts to lose horsepower around 7000 feet or so (with stock boost levels as Mac indicated).

As you climb the turbo outlet temperatures rise for the same boost pressure so you also will lose power due to the higher intake temperature.

All turbine engines lose horsepower or thrust as they climb, just like a normally aspirated engine. Usually turbine engines (turboprops and jets) are derated. For example the Pratt & Whitney PW118A is normally rated for 2300hp but derated to 1800hp. They do that so it will be able to maintain it's "rated" horsepower up to a higher altitude.

Rolls Royce Merlin (piston) engines used a two stage supercharger if I remember correctly. As the pilot climbed up they switched the supercharger over to "high" which allowed the engine to make the same hp all the way up to high altitude.

Some piston engines were called compound engines, meaning they were both supercharged and turbocharged. The Lockheed Constellation used compound engines, I've even read about a Toyota MR2 that was compound.

After all that babble, you will notice a little loss of low end horsepower but your car will still make the same peak power in Denver. It will be more sensitive to temperature increases though. If your car was normally aspirated it would only make about 75% of it's rated power in Denver.
 

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The ECU measures mass flow (MAF); the other parameters such as boost pressure are adjusted to provide the desired mass flow. The steady-state power would be largely unaffected at higher altitudes except that the intercooler loses efficiency due to the reduced mass flow of the cooling air due to the lower ambient air pressure. This would affect performance most on warm days.

Turbosupercharged is the proper name for a turbocharged, it is not a compound setup. Turboprops and turbine engines have precious little to do with the turbocharged intercooled reciprocating engine in a Passat.
 

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GH is correct, the ECU also measures intake air temperature (IAT) and detonation. At higher elevations a 1.8T is going to have higher IATs which will cause the ECU to retard timing and eventually retard boost. So there are a lot of factors causing you to lose horsepower. Our little turbos are working pretty hard even at one mile high.

Turbos are just exhaust driven Superchargers which is where the term turbosupercharged comes from so I definately see your point.

I realize turbine engines have very little to do with the 1.8T in a Volkswagen. People are usually surprised to learn that turbine engines lose horsepower just like a normally aspirated engine. I think people associate turbines with turbos thinking they can produce rated power at high altitude. Since someone brought up the subject in a previous post I thought it would at least be interesting information to share.
 

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Discussion Starter #11
cool good info!

I guess my FMIC will help me out afterall
 
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