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      05-11-2010, 07:19 PM   #1
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Power loss at elevation question.

I live at 4500 ft.

What crank hp would I get with 91 octane w/S65 motor
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      05-11-2010, 07:26 PM   #2
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      05-11-2010, 07:37 PM   #3
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I'm not a noob but I was arguing this point with the sales mgr here in utah. Wanted to ask the experts.

I told him I think it's about a 13.5% loss or about 360 crank hp and he says his techs have measured it at a 8% loss or about 385 hp.

Last edited by Cornhusker; 05-11-2010 at 08:04 PM.
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      05-11-2010, 07:40 PM   #4
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Based upon SAE calculations, you are looking at ~18% loss in power...
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      05-11-2010, 07:43 PM   #5
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Quote:
Originally Posted by mixja View Post
Based upon SAE calculations, you are looking at ~18% loss in power...
Thanks, anyone else have any actual evidence of losses at around 4500 ft?

BTW, went to NZ few years ago, loved the south island and the vocanoes you have there in the N. island.
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      05-12-2010, 06:53 AM   #6
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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
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      05-12-2010, 11:13 PM   #7
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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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      05-13-2010, 04:42 AM   #8
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Quote:
Originally Posted by mixja View Post
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.
this works well, but it over compensates slightly.

If I use the constants and only put my altitude of 5300 ft, it gives me a calculated air pressure of 24,03 in Hg. But at my location now the actual air pressure is 25 in Hg. It also shows a 22% loss of 78% of sea level power, which is over by 3-4%

You need to get the corrected to sea level pressure from your local air port or weather station for the day and plug that in. You also must input the humidity. When you do this it will make the percentage loss slightly less, and is more accurate to real wold conditions

The easiest and most accurate method is to divide the sea level air pressure by the actual air pressure at your altitude to get your % ratio

otherwise your correction formula will cause an inflated figure for sea level.

In actual environment, I have a 6psi pulley on my charger but at 5300 it read 4,78psi, roughly 82%
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