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      05-12-2010, 11:13 PM   #7
mixja
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Drives: 2011 E90 DCT Silverstone
Join Date: Jun 2008
Location: Beverly Hils, CA

Posts: 783
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Quote:
Originally Posted by Bob MG View Post
I have worked this out to absolute 100% accuracy for my SC thread:

http://www.m3post.com/forums/showthr...=374270&page=3

Sea level pressure 1019hpa THIS IS CONSTANT
You work out your air pressure at your altitude. Check with a weather staion if you dont know how

At 4500 ft pressure its approx 865hpa (this can be worked out for any altitude)

The percentage of air pressure at 4500ft compared to sea level is *
derived by 865/1019 = 0,848


Therefore at 4500, you lose exactly 15,5%
Take the factory rated power of the M3 at sea level 320 whp * 0,848 = 271,36 whp

Crank HP 410 HP x 0,848 = 347HP
Go to http://www.csgnetwork.com/relhumhpcalc.html

Plug in standard condition values (i.e. the values that give "Calculated Relative Horsepower To Rated" value of 100%):

Air Temperature - 77F
Ambient Pressure - 29.235 inHg
Relative Humidity - 0%
Elevation - 0 feet

Now keeping all other parameters constant, change the elevation. You'll see that the "Calculated Relative Horsepower To Rated" drops to 82.5% - i.e. indicating a loss of 17.5% due to elevation.
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