one major problem with using barometric air pressure readings is that they
are 'corrected' for altitude ... i.e.my barometer here reads 1.0 atm, but
its really .95 atm absolute pressure (1.0 atm would be at sea level) ...
it's really messed up but the reason they do that is so weather guys don't
get confused. Best thing would be if the track you were at has an absolute
pressure gauge. That's the key .. it has to be absolute without any
altitude correction.
Check out these websites for conversion factors though:
http://www.gnttype.org/techarea/misc/altitude.html
http://www.nhra.com/tech_specs/altitude.html
-- Canuck -------------------------------------------- Y2K, 4.7L, 2wd, 5spd, The Ultimate K&N HomeBrew, Flowmaster CatBack, Home Ported TB, Electric fan conversion, 180 therm., Redline synth., IAT relocate, HO Cams, HO Intake waitng for install http://www.twistedbits.net/WWWProfile/dakota/Vyikam1jjgNN6<jon@dakota-truck.net> wrote in message news:annp9g$jq1$1@bent.twistedbits.net... > > "scsilverdak" <scsilverdak@hotmail.com> wrote: > > : My testing of my Dakota this past summer has yielded a few questions, just > : how much does the altitude of a dragstrip have an effect on the way a car or > : truck will actually perform? > : Say given that the weather and track conditions of 2 different tracks were > : the same, but the track with a altitude closer to sea level would enable > : said car or truck to ET better due to better air quality. > : Is there a correction factor that would give some idea > : how a car or truck would perform at a lower sea level?...........or am I > : just nut's thinking the Dakota > : would run better a lower level track? > : Keystone has altitude of 1500ft above sea level, I'm betting the Dakota > : would ET better at a track with a level of around 500-800 ft. > > > > This is almost a religious issue with some folks ;-) but here is > my take on it... > > I ignore elevation because elevation itself doesn't have an effect > on your performance. Where elevation does come into play is with the > air density - the higher you go, the less the "column of air" pushing > down on you weighs, and the less the air pressure. However, this is > nothing more than barometric pressure. This is why I ignore elevation > and base everything on weather readings (temp, humidity, barometric > pressure) > > A little example might be more enlightening... Say you went to > a sea level dragstrip and made a pass. At the time you made the run, > the temp was 60 degrees, 50% humidity, and a barometric pressure of 30". > Now, you go to a strip where everything is identical except this one > is at 5,000' elevation. The temp is 60 degrees, you have 50% humidity, > and tha barometer is reading 30". For the sake of argument, imagine > that everything else is exactly the same as the other run (track surface > and truck condition, etc.) Would you expect to run faster, slower, or > the same as before? The answer is the same - even though the elevation > is much higher which is detrimental to performance, the local weather > conditions compensated and raised the barometric pressure up to the same > pressure as at the sea level track. > > This is why I don't pay any attention to elevation - although it > does have an effect on barometric pressure, I read the pressure > directly off the barometer, and I don't care a bit about what > is contributing to that pressure, all I care about is the end > result. > > Another way of looking at this from my perspective would be to > consider running at a strip where the air temp is 80 degrees. > Suddenly some clouds roll in and the temperature starts to drop. > Do you run for a light meter or a cloud chart to try to extrapolate > how much effect these clouds are having on the air temperature? > No - you just read the thermometer. That's all you care about - > the end result. Likewise, elevation is simply a factor, like the > clouds were simply a factor. All you need to be concerned with > is the end result, and reading the barometer will give that to you. > > I don't like to use elevation, because it can be misleading. It > is only one of the factors that contributes to your overall performance; > temperature and humidity are important as well. Using the actual > temp, humidity, and barometric pressure readings, you can use > conversion factors to correct your ETs to "standard" - elevation is > simply not a factor for anyone who has a barometer. (And anyone who > is trying to "correct" their times without a barometer, relying simply > on elevation is only fooling themselves - garbage in, garbage out.) > > That said, in general, yes, you will run slower at higher elevations. > :-) > > > -- > > -Jon- > > .---- Jon Steiger ------ jon@dakota-truck.net or jon@jonsteiger.com -----. > | I'm the: AOPA, DoD, EAA, NMA, NRA, SPA, USUA. Rec & UL Pilot - SEL | > | '70 Barracuda, '92 Ram 4x4, '96 Dakota, '96 Intruder 1400, '96 FireFly | > `----------------------------------------- http://www.jonsteiger.com ----'
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