Power loss at altitude with a Turbocharged engine

[sarends]

Does anyone know how much power a turbo charged motor loses as altitude increases compared to a normally aspirated motor?

I have heard that a rule of thumb for power loss on a normally aspirated motor is 3% for every 1,000 feet of elevation above sea level. I live at 6,000 feet here in Colorado, so if this is true, my normal 400 horsepower M5 would be down 18% (6 x 3%) or 72 HP netting 328HP.

Does a turbocharged (or supercharged) engine suffer less? Can anyone point to any specific studies or graphs, etc.?

Regards, Steve

[Skaala]

well, in WW2 the fighter airplanes with supercharged or turbo engines had much better high altitude performance.

[sarends]

I still have not found out the comaprative loss differences between normally aspirated motors and force inducted motors. My progress so far:

I used the calculator at this web site:

http://wahiduddin.net/calc/calc_hp_dp.htm

. . . to build this Google spreadsheet:

http://spreadsheets.google.com/ccc?key=pdoaJfYHNVTngZO_BvcDPDw

Please feel free to insert your car's beginning horsepower at sea level in cell D2. Then, find your elevation in column B and read across to obtain your (approximate) adjusted horsepower.

I have no idea how accurate what I have come up with is. If the calculator found at http://wahiduddin.net is accurate, then I have a high degree of (mathematical) confidence that the Google spreadsheet is reliable.

My conclusions so far:

1) Assume that my stock e39 M5 has 394 HP at sea level (with dew point and humidity that is not detrimental)

2) I live in Highlands Ranch CO at 6,000 feet

3) According to the Google spreadsheet (derived using the wahiduddin calculator, an engine will produce 76.9% of it's sea level altitude at an altitude of 6,000 geet

4) Therefore my M5 is making horsepower of (approximately) 303.0 in Highlands Ranch (6,000 ft) CO.

I hope this is helpful!

[JavierNuvolari]

That is SO cool!!, thanks for sharing that sheet, I'm sure that a lot users will benefit from it .

Peace,


Javier

[Skaala]

do you need a google account?

[sarends]

Nope - just paste the URL into your browser. - Steve

do you need a google account?

[SoCal]

Steve,

Very cool spreadsheet.

In answer to your specific question, turbo manufacturer (BorgWarner) says this:

"The high-altitude performance of a turbocharged engine is significantly better. Because of the lower air pressure at high altitudes, the power loss of a naturally aspirated engine is considerable. In contrast, the performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss."
Source: http://www.turbodriven.com/en/turbofacts/advantages.asp

[gregoryindiana]

I wish I could cite an authoritative source, but there is a point where turbos at altitude reach the limit for the turbine blades rpm. They can't go any faster without going supersonic. So at that altitude the turbo is limited, and any higher the boost will drop off. I think it is above 10,000 feet, though.

Any other experts comments??

[chewym]

Turbocharged engines lose much, much, much less power at altitude than naturally aspirated engines with similar power levels. The very regular VW/Audi 1.8 T with 170 hp does great in the mountains, regular 4 cylinders with similar power are left in the dust and larger V6 lose all of their advantage.