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Re: Cool weather tune up? [Re: 440Jim] #1090333
10/10/11 11:24 AM
10/10/11 11:24 AM
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tboomer Offline OP
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I used the Drag Times one,Jim...That is how I got my numbers from the last time out..


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Re: Cool weather tune up? [Re: tboomer] #1090334
10/10/11 11:26 AM
10/10/11 11:26 AM
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440Jim Offline
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Yes, Drag Times uses the reported barometer (which is corrected to sealevel). They have the track's elevation and their calcuation changes the reported barometer to actual barometer based on elevation (like I did).

And their numbers are useful if you have no track measurements. But since they are not temp and humidity from the track, they can be off the actual due to local conditions:
-the airport cools/heats faster/slower than the track
-the track's pavement (acres) might cause locally higher temps
-the track's location might have different humidity (nearby river, lake, etc.
IMO, the baro correction is pretty good (if the track elevation is correct) since that doesn't change much over 10-20 miles. But clouds can shade the track (or airport) and with the pavement have 5-10 degree different temps (worst case)

Re: Cool weather tune up? [Re: 440Jim] #1090335
10/10/11 11:30 AM
10/10/11 11:30 AM
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I may go back thru my logbook and put some figures in from warm weather...That may be interesting!!


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Re: Cool weather tune up? [Re: 440Jim] #1090336
10/10/11 11:59 AM
10/10/11 11:59 AM
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440Jim Offline
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Here is an example Maryland International Raceway, 10/8/2011, 11:30 am:

Actual track measurements: 69ºF, 43%RH, 30.45"Hg, calc 184 ft DA (80 ft track elevation).

Drag Times: 66ºF, 56%RH, 30.54"Hg, their calc 33 ft DA (87 ft track elevation)

-------------------------------------------------------
9pm
Track Measure: 54ºF, 97%RH, 30.39"Hg, calc -690 ft DA
Drag Times: 52ºF, 82%RH, 30.49"Hg, -881 ft DA

The other thing to note was that the actual performance didn't change as much as the DA might indicate. A 900 ft change in DA might indicate an ET change of 0.09 seconds (gas, normally aspirated), but nobody saw that much. That is my feeling about the equations not reflecting the actual humidity effects.
FWIW, my car went 5.778 at 11:30am and 5.794 at 9pm. (not bad)
All runs (in order) 5.778, 5.790, 5.788, 5.790, 5.792, 5.794 (lost -0.001 red)
Gas cars change more due to temp, alcohol due to humidity.

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