Temp, Humidity, Elevation, Barometric Pressure information

[j_evo2003]

Site suggestion. You guys have a spot for inputting temperature, but temperature is only part of the equation. Barometric pressure is the biggest influence over how much power a car is making on any single day. Check out this site. http://findarticles.com/p/articles/mi_qa40...306/ai_n9240601

Listed in order of highest importance to drag racing
1. Barometric Pressure
1a. Elevation, which kinda follows pressure
2. Temperature
3. Humidity

[grumpy]

Not everyone carries a weather station with them to the track. I know quite a few racers who do, but a vast majority of us week-end wanna-be's don't. They are either too expensive or we just are not at the point where it matters in our tune-ups. In an ideal world, the e.t. slip would provide that info, but we don't live in an ideal world.

[BMan1113VR]

Site suggestion. You guys have a spot for inputting temperature, but temperature is only part of the equation. Barometric pressure is the biggest influence over how much power a car is making on any single day. Check out this site. http://findarticles.com/p/articles/mi_qa40...306/ai_n9240601

Listed in order of highest importance to drag racing
1. Barometric Pressure
1a. Elevation, which kinda follows pressure
2. Temperature
3. Humidity
[/b]

Some tracks provide temp and humidity readouts on their timeslips. Elevation is non-negotiable; it doesn't change daily. . .Preassure. . .well thats going to be hard to work out.

I'm looking into adding the track elevations to the track tables, so if we know which track they ran at, we know the elevation. I can add pressure and humidity, but it would be a very small number of people who would have the data, and even smaller that actually put it in.....

[Rhansen]

You can get much of the necessary data if you have a date/time and location from the timeslip. Just go here - http://www.wunderground.com/history/airpor...eq_statename=NA - and look up the (closest) location and time to get the data. Since the baro. reading is "sea level" you will not need an elevation, just input the data into a calculator like this - http://users.erols.com/srweiss/calcda.htm - and you will have a reasonable estimate of density altitude.
Of course every track SHOULD put this info on the timeslip, but it's not a perfect world.

[j_evo2003]

You can get much of the necessary data if you have a date/time and location from the timeslip. Just go here - http://www.wunderground.com/history/airpor...eq_statename=NA - and look up the (closest) location and time to get the data. Since the baro. reading is "sea level" you will not need an elevation, just input the data into a calculator like this - http://users.erols.com/srweiss/calcda.htm - and you will have a reasonable estimate of density altitude.
Of course every track SHOULD put this info on the timeslip, but it's not a perfect world.
[/b]

Very nice! Thanks for the links.

[Deborah-WFO]

This is a great food for thought ariticle- Thanks!. Howver it barely scratches the surface in what you should really know about weather. A humidity reading is a relative measurement. If you notice, the article later talks about molecules of oxygen. Racers who tune by the weather are less concerned with humidity and more concerned with molecules of oxygen versus grains of water in the air. If you are going to measure weather, reading the forcast is not really helpful because the condition at the track is not the same. Additionally, the weather changes through out the day. One of the real tell tale weather measurements is the Altitude Density. Minus 1100 feet is unheard of go fast weather. The lower the altitude density, the better the air is for running fast. Barometric pressure is an indicator of cylinder pressure thus turning into a measurement of horsepower to define it very briefly. Weather tuning is an absolute must for nitrous cars. Ever wonder why these cars all run great one race and the next time everyone has burned pistons. Weather is your answer. Using the weather to tune in combination with other factors can be very effective. Understand that weather tuning takes conbinations of weather factors into account, which translate into different meanings at different times depending on your application.

http://www.worldsfastestorganization.com
http://www.loperspeed.com

[Rhansen]

I had a request (on another site) to dig up the raw formulas for DA from temp., hum., and baro. press. so I thought I would revisit this thread and post them up. FWIW the online sources for these formulas can be confusing and inaccurate (in the case of NOAA).

^ indicates an exponent
x indicates multiplication
/ indicates division
( ) indicate grouping symbols
+ indicates addition
- indicates subtraction or a negative value

the above may be redundant but I included it to avoid any confusion.
The formulas are setup for inputs of temp in farenheit, barometer in inches and humidity as a decimal.

F = temp in farenheit
(5/9)(F-32)=C
6.1078x10^((7.5xC)/(237.3+C))=S
H=humidity as a decimal
SxH=E (=vapor press in MB)
LN = natural logarithm
(-430+237.7xLN(E))/(-LN(E)+19.08)=D (=dewpoint in celsius)
I = barometer in inches
Ix33.8693=P
(C+273.15)/(1-.378(E/P))=K
Ix3386.389=L
44.3308-11.1802(L/K)^.234969=M
Mx3280.83333=X (=density altitude in feet)

Given a calculator and cheap weather station you can figure DA at the track. If you do some data collection, you could write a regression equation to act as an ET predictor.

great info, I've been looking for something like this, I'm going to see if I can create a DA calculator using the formula in PHP.....

thanks!

DA Calculator is up....

http://www.dragtimes.com/da-density-...calculator.php