DA vs Temperature

[Andy13186]

I have a question about DA vs temperature. I am wondering if -1000 DA in 50 degree weather is exactly the same in terms of performance as -1000 DA in 35 degree weather? Will a car be faster in the cooler temps or does that not matter if the DA is the same?

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[WildHorse]

In a nutshell Colder temps = more horsepower

 

[Rental18GT]

I have a question about DA vs temperature. I am wondering if -1000 DA in 50 degree weather is exactly the same in terms of performance as -1000 DA in 35 degree weather? Will a car be faster in the cooler temps or does that not matter if the DA is the same?

Density altitude is the end function of all conditions. If you have two different temperatures but the same DA, that means other factors are different. Humidity, barometric pressure, etc. If you have a 70* day with 20% humidity and the DA is +1000ft and then a 55* day with 70% humidity and the DA is +1000ft, the air density is the same. Sure the air may be cooler but there is an outside influence effecting the density of the air. The car will run the same if the DA is the same.

 

[WildHorse]

Density is directly proportional to pressure and indirectly proportional to temperature & humidity.

p = air pressure (hPa) (kg m-1 s-2) V = air volume (m3) R = universal gas constant for dry air (287 J kg-1 K-1) T = air temperature (K)

For atmospheric applications, however, volume is not well defined, and since density is mass per volume, using atmospheric mass and volume, the Gas Law can be reformulated:

p = ρRT where ρ = air density therefore ρ = p R-1 T-1. So for every 3 degree increase in temp, the pressure decreases 1%.

 

[andrewtac]

using my DA calc app
T=35, P=29.40, DA = -1003, SAE HP =1000 gives 1056.2
T=50, P=30.29, DA=-1001, SAE HP=1000 gives 1075.2
I used 0% humidity. Not sure what the calculator is using, but this would indicate more dependent on pressure than temp. I found a correction factor formula, looks like temp changes by the square root and pressure is linear.

 

[andrewtac]

T=100, p=33.26 (I know impossible), DA=1000, SAEHP=1000 gives 1136.9

 

[drive_55_not]

T=100, p=33.26 (I know impossible), DA=1000, SAEHP=1000 gives 1136.9

I'd also say you'll never see a -1000 DA with 50f air temp's either.

One thing you're missing is dew point/water grains.

You'll make more power in 35' cold clear low dew point air over warmer air with the same dew point, Since water displaces all those big beautiful and cold O2 molecules,

 

[andrewtac]

I'd also say you'll never see a -1000 DA with 50f air temp's either.

One thing you're missing is dew point/water grains.

You'll make more power in 35' cold clear low dew point air over warmer air with the same dew point, Since water displaces all those big beautiful and cold O2 molecules,

Not true on the 50 and -1000. I have a time slip that days otherwise, well it was 47.

Plug some values in the calculator. Humidity doesn't affect it as much as pressure does.

 

[andrewtac]

Not true on the 50 and -1000. I have a time slip that days otherwise, well it was 47.

Plug some values in the calculator. Humidity doesn't affect it as much as pressure does.

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