Has anyone kept good records of the air density at the past two Nats? I beginning to log air density, but would like a head start in ET prediciton by using some data from my previously logged runs (I ran the same combos in 2001 & 2002). I need the density during your various runs on Saturday 2002, and on Thursday & Saturday 2001. Thanks for any assistance.
I saw Fred Catlin with a high dollar air meter taking samples of the air. I don't have the # to get a hold of him but I'm sure someone here does.
If you have a weather station and compare it to someone else's station, you will find varied readings for the same air. Track conditions (not weather conditions) will be different from year to year. I would be hesitant to use data from different years to setup your weather computer. The way I understand, some computers use calculations involving dyno correction factors, and then apply these HP values to the 1/4 mile to predict ET. The newer (and better, IMHO) computers use data from reference runs from your car to setup your "specific" weather sensitivity curve. If their are ANY other varibles other than weather, your setup will be flawed and it won't accurately predict ET. It is best to go to the track with only weather on your mind and stay all day to get a wide differential in weather conditions. Don't change jets, timing, burnout procedure, shift points, air pressure, etc. Run only in the same lane and don't use any runs that have 60' times that vary much. When you get home with a pile of time slips, then you can analyize them and find the perfect 2 or 3 to use as your "reference runs". Sorry if you knew all of this already, but I can get more detailed if you desire. What kind of weather station do you have? Does it use a small prgrammable calculator? Jeff Peoples
:grin: Hi Jeff. I don't know EVERYTHING (almost everyhing). Actually, I don't have a professional weather station. I have a relative air density calculator downloaded onto my Palm Pilot. It's not going to be very accurate, since it doesn't incorporate dewpoint or elevation in the calc. It uses temp, humidity, and barometric pressure (altitude adjusted). I basically wanted to take the old weather data, calculate the relative air density or RAD, and then plot my ET or MPH vs. RAD on Excel and see how close the correlation was (R squared; no I'm not a statistician BTW). Excel also calculates the formula for the best fit line to where for any RAD, it'll spit out a future ET or MPH. I figured after 3 days at BG (Thurs & Sat 2001 and Sat 2002) with widely varying weather, I could get a set of semi-useful trends. My runs on all 3 days were the exact same combo, except for the fuel (same octane, different oil company). Oddly enough, only 2 runs were made in the left lane, all others were in the right. You're probably right about the accuracy Jeff. I'd like to give it a shot and post the results if anyone is interested. I may even send the spreadsheet and a link to the Palm download to the GNTType list if anyone there is interested enough to. Those new stations are amazing. Do you run one?
If I remember correctly, in Bowling green in 2001, I think we calculated air density in the early part of the week at around 3400 to 3700 feet, it was really hot and humid. I don't know what it was on saturday because that's when the rear axle broke on my 62 special, I know the air was much better on saturday morning than on the rest of the days. Jim Burek
weather Armin I have weather data from my TAG system weather station from the 2001 and 2002 nats,let me accumulate the info and I'll post or email for you.As Jeff said,different stations will produce different data,its really all just relative to your own station as long as you use the same one all the time.In fact,last year the track included weather data on the time sheets and they differed from my station,but again its all relative so I just compare my data and was able to dial accordingly. gary (can't ignore the thumper 2 car)
Dude! Sounds like you've got a great setup. I'll bet it is better than you might think. I have a B&G weather station/computer. It has an altimeter, and a digital temp/humidity gauge. These are the only three things "measured". It also has a Sharp PC-1270 that has a ROM chip containing the programs for Density Altitude, dyno correction factor, density factor, barrometric pressure, vapor pressure, etc. If you think about it, these are all just different ways of expressing "air quality". They are all just a calculated number that combines the affects of air pressure, air temp, and air humidity. I wish I had my documentation handy, but if my memory serves me correctly, air pressure is the biggest and most important parameter, then temp, then humidity. We are both measuring the same 3 items and your PDA program probably calulates the air quality about like my Sharp, so your accuracy may be great. The way I understand it, dewpoint is controlled by temp a nd humidity, so you are taking into account dewpoint. Also, elevation is measured by the barometer (not how many feet above sea level physically), so you are taking into elevation too. So, you've got the bases covered. My bet is that your "relative air density" is the same as my "density altitude". I've heard it called "corrected altitude" also. You are right on target with the excel graph. My little computer is simply calculating the slope of the graph based on two "reference runs" and using that ratio to predict ET. If you use bad reference runs, you will most certaining get a bad predicted ET. This is why it is so important to use runs were ONLY the weather changed. This means the runs have to be with the same tune up, on the same day, with same track conditions. So if they VHT the track and your car likes it, you can't use one run before the VHT and one run after the VHT. Since there is no way the track can be prepared the exact same from day to day (much less year to year), it important look at your 60' times. If they vary alot, then you either have a traction problem or the track was different. The weather by itself won't really affect your 60' times that much. A guide line would be .01 seconds in 60' per 1000' change in RAD. So if you had a 1.50 sec 60' at 1000' RAD and a 1.53 sec 60' at 4000' RAD, your car and the track are consistant. Only the weather caused the variation. If there are a few runs that has inconsistant 60', don't use them in your program. If you can pick 3 or 4 runs and they all follow a straight line on your graph, then your in business! If a run is way off the line, something else probably happened to spoil the run. You've probably heard the old computer nerd (I am one!) saying "garbage in - garbage out". Its really true. Also the slope of the line on your graph will be affected by how rich or lean your running the carb. If you change jets, start over with the weather program. Alky also flattens the curve, you've probably heard that alcohol cars are not as sensitive to weather changes. Lots of serious bracket racers here use alky. I would love to see the results of your analysis, so please post them if you can. Sorry for the long post, but this is some really good stuff that can win you some races! Jeff
weather Ramin Heres the poop: Bowling Green on 6/14/01 93* 29.58 BP 50% hum air density 3074 ft 97* 29.56BP 41 % hum air density 3360 BG on 6/17/01 92* 89* 81* 29.76BP 29.70 29.68 42% hum 55% 65% air den 2661 ft 2496 ft 2055 BG on5/18/02 51* 58* 67* 66* 29.67BP 29.68 29.68 29.68 72% hum 58% 45% 37% air den 22 ft 412 ft 920ft 880 ft hope this helps gary
Thanks a ton Gary for your continued tid-bits of great help. I will let you all know the results whether I find out anything meaningful or not. Jeff and anyone else who's interested, although I don't have the web address of the site where I got the PDA free-ware download to calculate Relative Air Density, you can probably do an Internet search for the following key words: "Stephen T. Bacon" (the guy who wrote it) "Kory Gill" (the guy who did the calcs) "Jetting 2-stroke GP racing motorcycles" (the main topic of the site). Hope this helps.
Well, I said I'd post when I tried it out. Unfortunately, I had no luck getting much correlation at all. I tried jacking with ET some to adjust for different 60fts I got and still no good. Oh well, it was interesting. I will probably try a few more things after I gather more track data and will post any significant findings. Thanks to all for your comments and help!o No:
