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09062016, 05:28 PM  #1 
Scooby Newbie
Member#: 335243
Join Date: Oct 2012
Chapter/Region:
TriState
Location: Nyack, NY
Vehicle:13 WRX SWP 
Density Altitude
Long story short, I ran 12.153 at Island Dragway in NJ this weekend. A friend of mine said if I was at Englishtown NJ (Raceway park) I would probably be in the 11's. I asked why and he said youre faster at Englishtown because its at a lower altitude.
So i looked it up and island is about 2,440 DA and raceway park is 2,030 DA. Would 400 feet really swing .15 in either direction? I ran across this post from juice14 on a lexus forum. Seemed like an interesting read. _______________________________ I did this a couple of weeks ago, I just didnt have the time to post this. Thanks to Caymandive I was able to get some information form his drag strip journal and use it to answer some questions that i had about drag racing in the IS350... So using a a statistical software i ran some tests. the main variable taken into consideration was density altittude (DA)..... I wanted to know, not only if DA affects 1/4 mile times(because it obviously does), but by how much. and what times to expect on 1/4 mile on my IS350 according to the weather conditions. It is hard to explain what density altittude is, but it is basically an international standard of measuring the density of the air, humidity, elevation, and altimeter, all into one number. the lower the density altittude the faster the car will be (basically). usually the lower the temperature is the lower DA is. So I ran a regression, which is a statistical analysis that lets you forecast 1/4 mile times (in this case) and answer other questions. From caymandive's journal, I took all the 1/4 mile times and their respective Density Altutudes at the time of the runs. I only took IS350's I did not take ISF times. otherwise this test would be pointless. Here are the results: Regression Analysis: 1/4 mile time versus DA The regression equation is 1/4 mile time = 13.4 + 0.000137 DA Predictor Coef SE Coef T P Constant 13.3584 0.0258 516.78 0.000 DA 0.00013677 0.00002112 6.48 0.000 RSq = 53.8% Analysis of Variance Source DF SS MS F P Regression 1 1.0086 1.0086 41.93 0.000 Residual Error 36 0.8659 0.0241 Total 37 1.8745 So, what do these numbers mean: • Question: Does density altitude have an effect on ¼ mile times? Yes, Density altitude does has an effect on ¼ mile times. Density altitude has a positive effect on ¼ mile times, which means that as density altitude goes up, so do ¼ mile times. And as density altitude goes down, so do ¼ mile times. There is only five percent chance that we have answered this question wrong, so we are 95% sure that these statements are true. • 53.8% of the variation in ¼ mile times can be explained by density altitude. The other 46.2% is explained by other factors such as: track conditions, driver’s skill level, weight reductions, tire psi, quality of tires, gas, head wind, tail wind, etc. So basically, 53.8% of your 1/4 mile time you can say its due to Density Altittude. the other 46.2% you can say, well this track sucks, or Im not a good driver, or my tires are old. blah blah, etc. • What times can I expect by looking at a specific DA number? With density altitude at 0 feet, the Lexus IS350 should run 13.4 1/4 mile E/T time. For every 1000 feet change in DA, there is a .13 second change in ¼ mile times. Example: You should run 13.40 @ 0 feet of DA. You should run 13.27 @ 1000 feet of DA. You should run 13.53 @ 1000 feet DA. This is how you can estimate your 1/4 mile time before going to the track by looking at the density altittude. example: if density altittude is 700...... you use the regression equation = 1/4 mile time = 13.4 + 0.000137 DA = 1/4 mile time = 13.4 + .000137(700) = 13.30 E/T time So, basically with Density Altitude at 700ft. I should run 13.3 on the 1/4 mile. anything lower than that is a good time. Important NOTE: remember most of these runs were done with intake/exhaust, and spare tire and jack removed. this will give the model some kind of error. ____________________________________ Do you drag race? Are you racing at high altitude? Notice that your times don't match other times you see on the net? Well, don't worry. There's nothing wrong with your car. It's ET is a little slower because the air at higher altitudes is less dense so your car's engine has less air during the combustion process. The NHRA uses a correction factor to compensate for altitude for stock/super stock classes. To accurately convert your ET, find your altitude with the chart below and convert your quarter mile ET and MPH to sea level times. Here's how you do it: Simply multiply the elapsed time factor below times your ET or MPH. ET Example: 16.1 x .9692 = 15.60412 corrected ET MPH Example: 84 x 1.0325 = 86.73 corrected MPH To find the elevation of the track where you drag race, check out the Geographical Nameserver. Enter the city, state and the server will find the info for you. and the altitude converters: Altitude(ft) ETFactor MPHFactor 1200 .9874 1.0129 1300 .9861 1.0143 1400 .9848 1.0157 1500 .9835 1.0171 1600 .9822 1.0185 1700 .9809 1.0199 1800 .9796 1.0213 1900 .9783 1.0227 2000 .9770 1.0241 2100 .9757 1.0255 2200 .9744 1.0269 2300 .9731 1.0283 2400 .9718 1.0297 2500 .9705 1.0311 2600 .9692 1.0325 2700 .9679 1.0339 2800 .9666 1.0353 2900 .9653 1.0367 3000 .9640 1.0381 3100 .9627 1.0395 3200 .9614 1.0409 3300 .9601 1.0423 3400 .9588 1.0437 3500 .9575 1.0451 3600 .9562 1.0465 3700 .9549 1.0479 3800 .9536 1.0493 3900 .9523 1.0507 4000 .9510 1.0521 4100 .9497 1.0535 4200 .9484 1.0549 4300 .9471 1.0563 4400 .9458 1.0577 4500 .9445 1.0591 4600 .9432 1.0605 4700 .9419 1.0619 4800 .9406 1.0633 4900 .9393 1.0647 5000 .9380 1.0661 5100 .9367 1.0675 5200 .9354 1.0689 5300 .9341 1.0703 5400 .9328 1.0717 5500 .9315 1.0731 5600 .9302 1.0745 5700 .9289 1.0759 5800 .9276 1.0787 5900 .9263 1.0787 6000 .9250 1.0801 this should be useful in comparing times since it levels it all and takes away the altitude differences.
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Last edited by dothatshht; 09062016 at 05:39 PM. 
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