[Camaro1973]

Originally Posted by synolimit

go to a shop and run on a dyno using the uncorrected factor. ask someone in say florida using uncorrected also with the same mods or whatever. that'll tell you the difference. however its not just about altitude so it'll be impossible to tell really but you could get close.

My 15 Z06 made 476 uncorrected and 553 corrected when I was in casper wyoming which is slightly less then denver as far as elevation.

[Snowwolfe]

Seems a lot of you are arguing over nothing. Isn’t the end result losing roughly 3% for every 1,000 foot of elevation?

[Camaro1973]

Originally Posted by Snowwolfe

Seems a lot of you are arguing over nothing. Isn’t the end result losing roughly 3% for every 1,000 foot of elevation?

No one is arguing. It's Close yes. I was just clarifying that 1 mile up, I lost roughly 14% at same elevation as denver, not 20%.

[7LitreC5]

Originally Posted by JSH

I've used 20% here today. Madcap in Lakewood told me they use 26%

I could easily see that on a 90-something degree day with humidity at our altitude.

[wnta1ss]

Dyno correction factors, which some guys are quoting, do not take whether the motor is NA or supercharged or turbo into account. This is a flaw which should not be overlooked. Another thing, the dyno correction factors were originally meant to account for different days in the Detroit area, like plus or minus 3% or so, and therefore they are not really in their intended range any longer when they are spitting out 20% corrections.

Here is another clue about NA vs supercharged at higher elevation, dragstrip ET correction factors for 5800 foot elevation (like the Bandimere track near Denver):
modded NA elapsed time correction factor is .9405
modded SC elapsed time correction factor is .9702

This smaller handicap for the supercharged motor shows us that the supercharged motor is not expected to lose as much power from the thinner air as a normally-aspirated motor is. Lose something, yes, just not as much.

If you REALLY wanted to know how much hp you've lost, you'd need to modify synolimit's dyno idea, by using a dyno on a trailer up there, printing both corrected and uncorrected sheets, then drive both that dyno and your car to low altitude and repeat the test. Same dyno, same car, high vs low altitude in other words. Look to see how much the actual hp at the 2 altitudes changes, and also what happens with the corrected numbers. Based on supercharged dyno sheets from high altitude that I've seen posted, I think you'd find that you did not really lose quite as much hp up there (actual vs actual) as the dyno CF seems to indicate.

[JSH]

Originally Posted by Snowwolfe

Seems a lot of you are arguing over nothing. Isn’t the end result losing roughly 3% for every 1,000 foot of elevation?

Most of us here can discuss such matters without attacking those who have a different opinion.


Yes, 2.5 to 3% for every 1000 ft. of density altitude is pretty close for discussion purposes.

Originally Posted by wnta1ss

Another thing, the dyno correction factors were originally meant to account for different days in the Detroit area, like plus or minus 3% or so, and therefore they are not really in their intended range any longer when they are spitting out 20% corrections.

This topic has been discussed here a lot. I agree, and as Dyno Jet told me last year, a dyno is intended to measure the power output of a particular car/build in a particular city and is not intended to make an accurate correction of that car's power in Denver to sea level.

Bone stock ZL1s up here are around one second slower than Chevy advertises.

[MatthewAMEL]

Superchargers and N/A motors lose power at the same rate due to atmospheric conditions.


Superchargers spin at a fixed rate relative to engine RPM since they are belt driven.


Turbos spin at a variable rate related to exhaust gases. It may take longer for a turbo to reach a given PSI, but it can spin faster to compensate. It's why the preferred method for FI aircraft piston engines is turbos.



And barometric pressure has nothing to do with power. The term you are looking for is 'partial pressure'. Since it's the O2 that causes combustion in the chamber, it's the amount of O2 in a given volume of air that matters...not it's absolute pressure.


Cars in Florida make the same power when the meter is 30.00 or 29.40.

[mariojas]

Originally Posted by MatthewAMEL

Superchargers and N/A motors lose power at the same rate due to atmospheric conditions.


Superchargers spin at a fixed rate relative to engine RPM since they are belt driven.


Turbos spin at a variable rate related to exhaust gases. It may take longer for a turbo to reach a given PSI, but it can spin faster to compensate. It's why the preferred method for FI aircraft piston engines is turbos.



And barometric pressure has nothing to do with power. The term you are looking for is 'partial pressure'. Since it's the O2 that causes combustion in the chamber, it's the amount of O2 in a given volume of air that matters...not it's absolute pressure.


Cars in Florida make the same power when the meter is 30.00 or 29.40.

But SC has pressure limit which means that (if RPM allow) maximum pressure will be the same, no?

[JSH]

There's no need to make this even more complicated. Atmospheric pressure is the sum of the partial pressures of its two gases - oxygen and nitrogen; and atmospheric pressure and oxygen pressure fall roughly linearly as altitude increases. No one in the history of internal combustion engine racing focuses on partial pressures.

Atmospheric pressure, or barometric pressure, is the key element of internal combustion engine power.

[MatthewAMEL]

Originally Posted by JSH

There's no need to make this even more complicated. Atmospheric pressure is the sum of the partial pressures of its two gases - oxygen and nitrogen; and atmospheric pressure and oxygen pressure fall roughly linearly as altitude increases. No one in the history of internal combustion engine racing focuses on partial pressures.

Atmospheric pressure, or barometric pressure, is the key element of internal combustion engine power.

You kinda got it, but you are way off when you say no one in racing focuses on partial pressure. You may know 'partial pressure' by it's common term...density altitude. Ask anyone who races if they care about the DA.

[JSH]

In summary, psia at 7000 ft elevation is 11.35, so:

11.35/14.7 = 77% of sea level atmospheric pressure in the intake manifold, or a 23% loss of power, even more than in Denver

Originally Posted by Camaroking98

Hey guys, been trying to do some research. Haven't really found a definitive answer or calculator...

I just moved to colorado (6700 feet) and I was wondering how I could calculate the power loss.

I've read that N/A loses the most power...then superchargers...and turbos are virtually unaffected.

Just wondering if you guys can help me properly guestimate how much power I'm losing up here.