How much can weather affect performance
07-19-2004, 02:20 PM
#1
AKA MaxGeek
Thread Starter
How much can weather affect performance
How much car warm/cold weather affect the engines performance?
I remember someone posting some general math about how much less/more hp you have depending on temperatures.
I remember someone posting some general math about how much less/more hp you have depending on temperatures.
07-19-2004, 02:43 PM
#2
Temperature, humidity and altitude will affect performance. I'm guessing you could lose from 2-5% in a large temperature changes and as much as 10% in extreme conditions.
07-19-2004, 02:51 PM
#3
Suzuka Master
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There are two issue, the relative air density and the ECU changes.
The one you cannot account for unless you know the ECU program is the reduction in ignition timing advance with increased intake air temperatures. This is certainly more than just a degree or two but the amount would be hard to trace without knowing the code or doing quite a bit of testing.
The other area is one which can be determined by getting the local weather information. The important thing to know is the relative air density which varies greatly with weather changes. I'll use two different examples, one hot humid day with a storm approaching and another cold, dry clear day.
Hot, Humid Summer Afternoon:
90 F Air Temp
90 % RH
29.5 InHG Baro
91.5 % Relative Air Density
1.057 SAE Dyno Correction Factor Multiplier
Cold, Dry and Clear Winter Day:
30 F Air Temp
30 % RH
30.2 InHG Baro
106.8 % Relative Air Density
0.913 SAE Dyno Correction Factor Multiplier
That alone is a 14.4% difference in power and still doesn't account for ECU timing changes. That could add another couple of percent possibly taking the total up to about 17% change. On a car making 250 uncorrected WHP on the cold day, it would only make 207.5 uncorrected. That is certainly a difference you would feel.
To a lesser extend we can use another example somewhere in beteen.
Fall or Spring Day:
60 F Air Temp
60 % RH
29.9 InHG Baro
99.3 % Relative Air Density
0.967 SAE Dyno Correction Factor Multiplier
Combined this with timning change and you get a difference of about 7% from the cold day or only 232 uncorrected WHP.
The one you cannot account for unless you know the ECU program is the reduction in ignition timing advance with increased intake air temperatures. This is certainly more than just a degree or two but the amount would be hard to trace without knowing the code or doing quite a bit of testing.
The other area is one which can be determined by getting the local weather information. The important thing to know is the relative air density which varies greatly with weather changes. I'll use two different examples, one hot humid day with a storm approaching and another cold, dry clear day.
Hot, Humid Summer Afternoon:
90 F Air Temp
90 % RH
29.5 InHG Baro
91.5 % Relative Air Density
1.057 SAE Dyno Correction Factor Multiplier
Cold, Dry and Clear Winter Day:
30 F Air Temp
30 % RH
30.2 InHG Baro
106.8 % Relative Air Density
0.913 SAE Dyno Correction Factor Multiplier
That alone is a 14.4% difference in power and still doesn't account for ECU timing changes. That could add another couple of percent possibly taking the total up to about 17% change. On a car making 250 uncorrected WHP on the cold day, it would only make 207.5 uncorrected. That is certainly a difference you would feel.
To a lesser extend we can use another example somewhere in beteen.
Fall or Spring Day:
60 F Air Temp
60 % RH
29.9 InHG Baro
99.3 % Relative Air Density
0.967 SAE Dyno Correction Factor Multiplier
Combined this with timning change and you get a difference of about 7% from the cold day or only 232 uncorrected WHP.
07-19-2004, 03:04 PM
#4
Instructor
Join Date: Jul 2003
Location: Los Angeles
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.. taking it to a more detail.... aside from air, humidty, ignition timing etc. your lubricant is at play here as well. When I tested my mechanical timepiece of 'high' quality [i.e. metal parts, constant friction against 39 jewels, same lubricant] religiously over 5 years... I noticed an interesting consistency... the piece was dead on the nose +3secs/day advance around warmer time, ie. spring/summer/early fall and -1sec/day during winter and colder months... And I am talking here much finer consistency lubricants... Of course humidity was not an aspect most of the time, since SoCal 
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