Roadrunner 45

iTrader: (1)

In the latest Hot Rod they mention that you CANNOT use the barometric pressure readings supplied by a weather service as they contain a correction factor based on what's "normal" at that elevation. They say that you must use "station" barometric pressure.

Besides buying a weather station like the ones in summit or Jeg's, is there another way to obtain the station barometric pressure?

kp

iTrader: (34)

I went around with that same question a while back. I ended up using NWS data and it seemed fairly consistant to what the car was running. If you use it for all your DA estimates it seems to work out. I used to use a weather station at the track but it was pre-internet so I really cant say how much difference there is but it sure seemed to always read a lot lower (higher DA) then using the corrected barometer.

The different pressures can get a little confusing sometimes

ChevyWeatherman

iTrader: (2)

http://www.mcs.drexel.edu/~dbrooks/globe/pressure.html

Based on weather report (METAR) pressure, you can find that actual pressure there. You need the elevation in meters. It says to enter the "weather report" pressure in millibars, but you can enter a in/Hg value and it will convert to millibars for you. If you want the actual track pressure back in in/Hg, you will have to convert it back from mb...and you can do that here: http://www.sciencemadesimple.net/EASYpressure.html

kp

iTrader: (34)

cool, I had found the 1st site a while back but had trouble easily converting mb back to inHg.

Roadrunner 45

iTrader: (1)

What about this site:

http://www.wahiduddin.net/calc/calc_da.htm

Looks to me like you put in your altitude and the weather forecast "version" of pressure and it spits out a DA#- the site also hase an "engine tuners" calculator based on DA.

Roadrunner 45

iTrader: (1)

I found this site which gives the elevation of airports around the country- (to use in the calculation from the DA calculator website:

http://www.airnav.com/airports/us

ChevyWeatherman

iTrader: (2)

Yeah, that one works for you lazy people.

McRat

Ok you math guys:

If it was 95 deg, 2200' physical altitude, with a 29.24 baro, and 25% humidity...

What factor would I use to correct my 11.89 sec ET?

86 IROC

iTrader: (14)

http://www.modulardepot.com/density.php This "should work", but gives the corrected #'s for your what your car "should" run at exactly perfect sea level conditions. HTH

Tom the roofer

iTrader: (9)

Here is the one I use. I found it works the best.

kp

iTrader: (34)

Quote from that site:

"The altimeter setting is the value in the altimeter's Kollsman window when the altimeter is set to correctly read a known elevation. The altimeter setting is generally included in NWS reports. The altimeter setting is not the same as the sea level corrected barometric pressure."

But if you go through all the calculations it comes out close enough. This is one of those subjects where the more you look into the more complicated it becomes. The site above is close enough for all practical purposes if you just uses NWS barometer.

In reality tom's weather station is the most accurate - what you run is what you run It is nice to correct down just to compare to others and cross check dyno numbers..

Coach 02 A3 Z/28

iTrader: (10)

Now that is SWEET!!!!!!!!!!!!!!!!!!!!!!

Coach

SilverGhost

iTrader: (53)

Tom the Roofer's looks to be more accurate than any chicago area weather report