juice14

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 IS-F 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

R-Sq = 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. But also remember mods dont do much for the IS350.

ToothDoc

So I'm a statistical outlier? My IS350 was totally stock. (no intake, exhaust, kept the spare and jack) and I'm kinda fat too. Good analysis juice14!!

juice14

Id say yes. but you would have to see what was the density altittude at the time of the run. do you remember, maybe temp? and elevation of track?
Also remember you are the Fastest stock IS350. so im gonna say you are an Outlier hehe.

combfilter

iTrader: (3)

He already knows the DA/ time/ temp / etc from his 13.28. There was a large thread and all of this has been in caymandives drag journal for a while.

you ran a 13.28 because you had -1110 DA and a 12mph tailwind. You had I believe the fastest 60' time of all as well. Great Lakes Dragaway like Cecil County (where caymandive ran his fastest) is also know to slope down at the end of the track. The original posters Point still stands true. DA is everything.

http://spreadsheets.google.com/pub?k...vrJeuOj2lAN-EQ

BTW toothdoc is your sig still true? I got a VM from caymandive the other day and I think he ran 12.44 if i remember right in his stock IS-F?

juice14

tail wind is part of the unexplained part of 1/4 mile times. which is 46.2%. the other 53.8% is directly explained by DA.
I will be testing the accuracy of this model in real life when i go to the track sometime in the next 3 weeks.
By knowing the DA i should be able to tell what i should i run. and end up having a time within .1 sec of the forecasted
maybe somebody looks at this and uses it to see how accurate it is.

juice14

I will be going to the track tonight and testing this model's accuracy.

Ive looked at my 13.67 time couple of months ago @ 2086 DA and I pluged the numbers in the formula to see what the model says you should run at 2086 ft of DA:

Time= 13.4 + .000137(2086)= 13.67

Low Life

iTrader: (1)

we had a NHRA even here in Utah last july, my track is 4424'ft. above sea level. And DA that day was 11,000ft! lets just say there were no records broken that day, my car runs 4 tenths slower than when i go to California, or New Jersey.

you guys wouldnt believe how slow cars are out here on midnight drag nights.
ive yet to see a is350 run, but to give you an idea of what cars run, my friends stock charger srt-8 went 14.05@98 stock 350z are around 14.8-15.0
cars just cant breath up here, plus our track is garbage

juice14

I couldnt go to the track tonight it rained.

HOLLY crap. 11,000 feet DA?????

ok lets plug it in the formula to see what the IS might run up there. LOL
1/4 mile time = 13.4 + .000137 (11,000) = 14.9 sec.....

since this number is so far away from the data that i had, it might not be as accurate, because the regression might not be linear. but its a rough estimate. Im guessing 14.9 is kinda right for an IS350 up there, since the 350Z's run high 14's. the IS350 should be a lil quicker than the 350Z maybe.

you should dyno your car see what you get. just courious.

ToothDoc

Hey, that's 13.228 not 13.28. LOL Actually, I've probably run down the strip close to a 100 times last year in my IS350. By posting the very BEST ET, I'm giving you my statistical outlier. On average, your formula works VERY well and something that several of us have always known but never analyzed statistically.

I don't really think GLD is particularly a fast track - I can't visibly see a downhill at all. BUT, on some days, the prep is pretty good - good to the point where I CAN'T spin at all by mashing the gas pedal. And that's pretty good considering I'm running an IS-F with lighter rims! (Hence the quick 60' times)

juice14

12.4 on your IS-F!!!!! if they come out with some mods for the IS-F you might hit 12 flat one day

caymandive

iTrader: (2)

Yeah we are all sick of the teaser mods for the IS-F. Release them already!

I do agree a 12.0 shouldn't be out of the question with some mods and sticky tires and a bit of weight reduction.

crazybuggy

omg so much math

juice14

I rode on a old 2003 m5 today and think the IS-F can get better times is crazy