znod

Hi B32:

I give the difference in 18" RFTs and 19" PS2's in the "Mind Candy" link in my sig. The unsprung equivalent is about 48 lbs. given my estimation methods. The difference would, of course, be larger if 18" PS2's were compared. You can get the differences you are interested in at tirerack.com. Before investigating things on this site, be sure and "save your car" first. Hot weather, as g-man mentions, is seriously retarding to wheel spin.

znod

Hi All:

I have done a pile of calculations. I won't burden you with the details. I have been dealing with two issues. First, I have continued to try to pinpoint the variation in HP, if any, attributable to the effects of weather. Using techniques along the lines I posted earlier, I think I can substantiate about an 11 flywheel hp loss over the range of weather conditions over which I have tested my car. Similarly, I think that I can substantiate about a 10 average flywheel hp loss over this range. Thus, weather adjustment, in addition to altitude adjustment, definitely is appropriate for our cars despite their engine management systems (i.e., which are supposed to minimize the effects of weather differences). Perhaps our engine management systems do a reasonable job since my density altitudes range from 787.90' to 3,384.90'--a difference of 2,597'.

These HP differences account for substantial portions of the time differences in my adjusted to 500' altitude data (and, similar, for my unadjusted data). For example, coincidentally, I have 24 tests both above and below my average density altitude of 1532.26' (which is approximately equal to my actual altitude of 1600'). In this regard, the altitude-adjusted average 1/4 ET for my 24 below average density altitude tests is 13.545 (I think the .545 part is especially poignant), while my altitude-adjusted average for the 24 above average density altitude tests is 13.596. The difference in these averages is .051, while the difference in the lowest value in the first average and the highest value in the second average is .278 = 13.700 - 13.422. Undoubtedly, random factors have had a major role in accounting for the .227 difference in .278 and .051. On the other hand, it is likely, without going in to detail, that my method of estimating flywheel HP losses understates the actual losses, perhaps significantly.

The second issue I have been pondering is whether 100% weather adjustment biases our results to a misleading extent for extreme weather conditions--as suggested earlier by grogan545 in the context of better than standard conditions. It is reasonable to suspect the presence of such biases assuming that our cars really do a decent job of minimizing the effects of weather differences and, as a corollary, that my method of estimating flywheel HP losses does not understate the actual losses significantly--since weather adjustments, like altitude adjustments, are linear. Keep in mind that if overstatements are occurring, then they would occur for all weather adjustments, but the effects of the overstatements would not become misleading until the adjustments become proportionately large. To this point, I have found no evidence of bias. I am continuing to investigate, however, because I have some seemingly odd results that I still am trying to explain.

I did find that application of the SMOKEmUP calculators may yield some totally insignificant errors. In assessing the significance of the errors, I developed my own ? more consistent" table for calculating weather and altitude adjusted results to 500?. I will be posting the table, along with needed instructions, soon. I checked my fully adjusted ET values using my table, found a few errors in my original calculations, and found that my table tends to produce ET results that are a few one thousandths slower that those of SMOKEmUP. I have not yet completely checked the effects on ? MPH.

In addition to the table, all you will need to do your own adjustments is density altitude (DA). I found a great source on density altitude?created by a sort of density altitude guru. I don?t imagine we will find more accurate DA calculators. Here is a link. Look on the left side of the page for the English-unit calculators. His site also has information on using DA in engine tuning and an English-unit tuning calculator, etc.

cobradav

Hi Znod,

Is this all part of the missing link program? oops its there now, but I cannot get to it from work. Will have to wait til I get home

znod

You are fast. Yes, the missing link program.

znod

I just checked out the speed calcs. They are very good too. Incidentially, I knew that I was producing very small conservative effects when developing my "more consistent" calculator.

znod

My calculator/table is coming soon.

Here are your raw and SMOKEmUP adjusted results from one of your passes.

Your results--Density Altitude:
Air Temp 72 (?F)
Altimeter Setting 29.96 (in)
Dew Point 63 (?F)
Altitude 20 (Feet)
Density Altitude 1080.3 (feet)

Your results--First Pass--Adjusted to Sea Level:
Density Altitude 1080.3 (feet)
Uncorrected ET 13.144 (sec)
Uncorrected MPH 111.88 (mph)
Corrected ET 12.995
Corrected MPH 113.179

Your results--First Pass--Adjusted to 500':
E.T. 12.995 (sec)
Trap Speed 113.179 (mph)
Measured DA 0 (feet)
Corrected to 500(feet) DA
Corrected ET 13.064 (sec)
Corrected Trap Speed 112.574 (mph)

Using "my" table, use the DA "right below" your calculated DA and, for example, in the above case, go:

Your Car Raw Score + {Your Car Raw Score[(My Car Raw Score/Your Car Raw Score)(DA/"Right-Below" DA)(ET or Speed Adjustment Factor)]} =

For ET: 13.144 + {13.144[(13.744/13.144)(1080.3/1050)(-.005820722)]} = 13.062

For Speed: 111.88 + {111.88[(102.898/111.88)(1080.3/1050)(.005937919)]} = 112.509

Note that the basic equation reduces simply to:

Your Car Raw Score + [(My Car Raw Score)(DA/"Right-Below" DA)(ET or Speed Adjustment Factor)]. "My Car Raw Score" always equals 13.744 for ET and 102.898 for speed.


Here are some results for g-man.

Your results:
Air Temp 40 (?F)
Altimeter Setting 29.8 (in)
Dew Point 18 (?F)
Altitude 400 (Feet)
Density Altitude -591 (feet)

Your results:
Density Altitude -591.0 (feet)
Uncorrected ET 13.35 (sec)
Uncorrected MPH 104.650 (mph)
Corrected ET 13.433
Corrected MPH 103.985

Your results:
E.T. 13.443 (sec)
Trap Speed 103.985 (mph)
Measured DA 0 (feet)
Corrected to 500(feet) DA
Corrected ET 13.514 (sec)
Corrected Trap Speed 103.429 (mph)

For ET: 13.35 + {13.35[(13.744/13.35)(-591.0/-600)(.011568685)]} = 13.507

For Speed: 104.65 + {104.65[(102.898/104.65)(-591.0/-600)(-.011798091)]} = 103.45

znod

Here is the promised table. Enjoy using it and the DA link I provided.

grogan545

Hi Zman.It looks like you have been busy.Thanks for the new correction chart,it looks like it is more conservative than the NHRA chart.I haven,t been posting lately,but have been reading the forum everyday.It looks like we are all tested out for now.I am waiting until after vacation(5-15 to 5-20) to do more testing.I think I will make one more trip to the dragstrip(hopefully 6-2)and make 4 runs and retire my 545 from active testing.If the weather doesn,t cooperate on 6-2,I will go when it is suitable.I hope to get all 4 runs on my GT2 also for a good comparison.I think I have found the limits of acceleration of my car and don't expect further improvement without modifications.However I still intend to stay abreast of all forum posts and respond in kind.

znod

Hokay g-man. I won't be doing much more in the way of testing until fall--when the weather starts to cool off. I'll be doing a little testing this summer just to see how our cars react to hot early mornings. It can be 100+ here before the sun comes up in August--90+ otherwise in the summer before sun up. I'll keep posting meter info as I still am trying to figure a few odd things out and to think more about whether partial weather adjustment might somehow be better than 100% adjustment. So, keep informed and let me know what you think about any of my musings. And, of course, let us know about your dragstrip trip. Best, Znod--the Zman.

Bimmer32

Man, you guys are getting too complicated for me. Actually, I don't have time to digest this awesome info. I'm going to have to take a vacation to fully understand this. :'( Good read. Thanks for all the testing. I wish I could do some testings too, but there's only 24 hrs in a day.