Density Altitude--DA?
Thread Starter
Safety Car
Joined: Sep 2002
Posts: 4,030
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From: Maryland
Density Altitude--DA?
? How do you calculate that, directly from the Barometric pressure?
Or does everyone look it up from the National Weather Service or something?
I would think the best times to race would be when the Barometric pressure is high, temp. cool, but with low humidity. Am I right?
Or does everyone look it up from the National Weather Service or something?
I would think the best times to race would be when the Barometric pressure is high, temp. cool, but with low humidity. Am I right?
Team Owner
Joined: Mar 2001
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From: Cincinnati, Oh USA
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Right you are, DA is the effective altitude based on weather conditions.
The hard core racers often carry weather stations that not only calculate DA but also predict ETs based on DA and prior passes.
The hard core racers often carry weather stations that not only calculate DA but also predict ETs based on DA and prior passes.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by sothpaw2
? I would think the best times to race would be when the Barometric pressure is high, temp. cool, but with low humidity. Am I right?
Race Director
Joined: Aug 2003
Posts: 13,421
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From: Lake Mary Florida
For future reference, density altitude is affected by pressure, temperature, humidity.
Low pressure, low temp, low humidity = low density altitude.
Opposite would be high.
So instead of your elevation being say 1200 feet above seal level, and those variables are mostly high, you may acutally be at say 1500 feet above seal level (density altitude). When the air is less dense, a high density altitude, your performance goes down because there is less air to compress (manifold pressure will be down).
Turbo charging the engine will remove most of the effects on performance as a result of density altitude.
Low pressure, low temp, low humidity = low density altitude.
Opposite would be high.
So instead of your elevation being say 1200 feet above seal level, and those variables are mostly high, you may acutally be at say 1500 feet above seal level (density altitude). When the air is less dense, a high density altitude, your performance goes down because there is less air to compress (manifold pressure will be down).
Turbo charging the engine will remove most of the effects on performance as a result of density altitude.
Former Vendor
Joined: Jun 2001
Posts: 7,204
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From: St Marys PA
This is the unit that most guys use. Its reasonably affordable and accurate. ~425 dollars.
It will calculate your DA, predict your runs etc.
Jetjockey. you will STILL see gains and losses with turbo and other powder adder setups, with changes in DA. Its not the "air" your seeing changes in, its the oxygen content of the air.
With low DAs there is more oxygen per cubic foot. Hot air can hold more water (humidity) which displaces the oxygen, and makes you run slower. Cold air conversely, has a harder time holding water (humidity), which allows more oxygen. Then Barometric pressure, plays a role also, which basically you can think of it as in higher BPs, its packing the oxygen tighter, which affords more oxygen to be present.
From our experiences, the humidity plays a larger role than anything else. Changes in the humidity often cause more changes in ET than other factors. BP is usually also a big player, but through the coarse of the day, it usually stays pretty steady. I mainly see BP changes from one track to another, which is usually cause of its physical reference to sea level (altitude). Closer to Sea level - higher the BP.
Hope that explains it to you better.
Jesse
It will calculate your DA, predict your runs etc.
Jetjockey. you will STILL see gains and losses with turbo and other powder adder setups, with changes in DA. Its not the "air" your seeing changes in, its the oxygen content of the air.
With low DAs there is more oxygen per cubic foot. Hot air can hold more water (humidity) which displaces the oxygen, and makes you run slower. Cold air conversely, has a harder time holding water (humidity), which allows more oxygen. Then Barometric pressure, plays a role also, which basically you can think of it as in higher BPs, its packing the oxygen tighter, which affords more oxygen to be present.
From our experiences, the humidity plays a larger role than anything else. Changes in the humidity often cause more changes in ET than other factors. BP is usually also a big player, but through the coarse of the day, it usually stays pretty steady. I mainly see BP changes from one track to another, which is usually cause of its physical reference to sea level (altitude). Closer to Sea level - higher the BP.
Hope that explains it to you better.
Jesse
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
Yep sorry I didn't get into real specific details as to why a specified volume of air is affected by DA. I just listed the components that affect DA, and a generalization or characterization of the effects.
