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Offline isiahstites

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Air density gauges?
« on: May 27, 2007, 03:52:00 AM »
How many people are using air density gauges while racing at LSR events? I have been reading up on tuning and this seems like an easy way to figure how many percent up or down you need to jet. Am I missing something?

I have searched here and found some info, however it seems like it could get real complex real quick.

Any info would be greatly appreciated.

Scott
« Last Edit: May 27, 2007, 12:09:19 PM by isiahstites »
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Offline Stainless1

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Re: Air density gauges?
« Reply #1 on: May 27, 2007, 09:05:42 PM »
Back in our carb days we chased density altitude with a passion.  It was really necessary with the afternoon qualifying and the next morning record run or runs.  Now we just check it and decide if we need to change the map a little...  :-)  Bringing our own altitude this year, hope it works out  :|
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Offline wolbrink471

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Re: Air density gauges?
« Reply #2 on: May 28, 2007, 09:23:59 AM »
Hello Stainless

Back in your ole carb days........

did you use an analog guage that swung a needle to the RAD number or did you wet bulb it and fight through the math??

thanks
Mark
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Offline Speed Limit 1000

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Re: Air density gauges?
« Reply #3 on: May 28, 2007, 12:30:16 PM »
Rick at ERC has a weather station and keeps records you can always check with him. :-D
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landracing

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Re: Air density gauges?
« Reply #4 on: May 28, 2007, 12:49:35 PM »
Here is a sample of what Rick has at ERC trailer.



jon
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Offline Harold Bettes

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Re: Air density gauges?
« Reply #5 on: May 28, 2007, 02:37:21 PM »
The devices in the pic are simple and effective. The digital baro is from VWR scientific and costs about $125.
The sling psychrometer (by Taylor) is also available from VWR and costs about $60.
The manifold pressure gage is from an aircraft boneyard and costs about $25.

The calculations for Air Density are easy to accomplish as are other atmospheric calculations that can use inputs from the simple instruments. However, if one uses the ERC trailer for a local weather station, that can be easily done as well.

Sorry, I couldn't get the pic to take.

Regards to All,
HB2
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Offline isiahstites

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Re: Air density gauges?
« Reply #6 on: May 28, 2007, 02:46:03 PM »
Thanks for all the posts!

Harold can you email the picture?

stites@cox.net

thanks,
Scott
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Offline Stainless1

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Re: Air density gauges?
« Reply #7 on: May 29, 2007, 12:03:40 AM »
Quote from: wolbrink471 on May 28, 2007, 09:23:59 AM
Hello Stainless

Back in your ole carb days........

did you use an analog guage that swung a needle to the RAD number or did you wet bulb it and fight through the math??

thanks
Mark

Mark, we had a simple weather station, temp, humidity, altimeter and a calculator.   :-o Usually cross checked our numbers with Ricks. Unfortunately Rick's updates were only a couple of times a day and I think one day I changed jets 3 times from being 10th in line to 3rd.  :|  (about 5 hours)  :roll:
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Offline Sumner

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Re: Air density gauges?
« Reply #8 on: May 29, 2007, 12:44:28 AM »
Quote from: Stainless1 on May 29, 2007, 12:03:40 AM
Quote from: wolbrink471 on May 28, 2007, 09:23:59 AM
Hello Stainless

Back in your ole carb days........

did you use an analog gauge that swung a needle to the RAD number or did you wet bulb it and fight through the math??
thanks
Mark

Mark, we had a simple weather station, temp, humidity, altimeter and a calculator.   :-o Usually cross checked our numbers with Ricks. Unfortunately Rick's updates were only a couple of times a day and I think one day I changed jets 3 times from being 10th in line to 3rd.  :|  (about 5 hours)  :roll:

I noticed a big difference in the readings at Rick's and a few hours later on the timing slip.  If you are going to try and work with air density I feel you need your own station and keep using that.  That's our plan this year.

I figure if I wet my finger and hold it up I'll be able to get wind direction, Humidity by watching how long it takes to dry and temp from past experiences in Wyoming  :roll:.  I'm working on the pressure thing  :cry:.

c ya,

Sum
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Offline wolbrink471

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Re: Air density gauges?
« Reply #9 on: May 29, 2007, 08:00:37 AM »
Thanks for all the input everybody....

From past experience, all the 'tools' measure their own way :wink: i wonder if anybody has tried to sit at the local university weather station and try to calibrate??

We were always careful to use the same gauge during dyno jetting as the one that would be used at the track. a benchmark was established...didn't really matter what the number actually was.We had a single face / analog gauge that was nearly as big as a gallon paint can. It rode in a beautiful mahogany or ???? wood case and never never never flew!

I understand the math, but reading a single number on the gauge and cross referencing a jet chart that is duct taped to the dial's cabinet seems easier / fool proof in the heat of it!

All that I can find to replace it are small 2 1/2 inch face dials at ~$125. Anybody have experience with these type and price point? or another suggestion???

Mark
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Offline Harold Bettes

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Re: Air density gauges?
« Reply #10 on: June 01, 2007, 08:58:06 PM »
Hey Guys,

A cheap thrill is using a $9 calculator and the following equation: 8-)

Dair = 1.325 (Pb / Tair) :lol:

Where Pb = local barometric pressure in inches of mercury ("Hg), Tair= Temperature of the local air, degrees F + 460 :roll:

Dair = lbs / ft3 :-o

Remember the local barometric pressure is not what the weatherman says as he uses CORRECTED numbers and your engine breathes only the local stuff, not corrected numbers. :?

Enjoy.

Regards to All,
HB2 :-D

You can keep track of how much the number varies in % when you are at any location.
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Offline Sumner

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Re: Air density gauges?
« Reply #11 on: June 02, 2007, 01:10:40 AM »
Quote from: Harold Bettes on June 01, 2007, 08:58:06 PM
Hey Guys,

A cheap thrill is using a $9 calculator and the following equation: 8-)

Dair = 1.325 (Pb / Tair) :lol:

Where Pb = local barometric pressure in inches of mercury ("Hg), Tair= Temperature of the local air, degrees F + 460 :roll:

Dair = lbs / ft3 :-o

Remember the local barometric pressure is not what the weatherman says as he uses CORRECTED numbers and your engine breathes only the local stuff, not corrected numbers. :?

Enjoy.

Regards to All,
HB2 :-D

You can keep track of how much the number varies in % when you are at any location.

Thanks.  Where does humidity come into play or is it not used in density altitude?

     

So on the timing slip I know the SP is the pressure.  Does the SP stand for station pressure??.............and are those the uncorrected numbers we should use??

Thanks,

Sum
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Offline Harold Bettes

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Re: Air density gauges?
« Reply #12 on: June 02, 2007, 12:44:26 PM »
Sum,

The simple equation that I initially chose to share does not address atmospheric water (vapor pressure, or relative humidity). The net effect of atmospheric water at such places as Bonneville has much less effect than baro or temp changes, it makes it easier to calculate by not addressing the water content. 8-)

You are correct, the SP is Station Pressure and should be an uncorrected number although if the reading is coming from a mercury barometer, there is a correction used for latitude and temperature effects on the mercury. This is for gravity correction and temperature on the mercury itself.  :lol:

I can include some other easy to calculate drivel if there is interest. Numbers mean something, but only if you know where the numbers come from. :roll:

Regards to All,
HB2 :-D
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Offline JackD

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Re: Air density gauges?
« Reply #13 on: June 02, 2007, 01:33:41 PM »
If you guys are really interesred in getting your beaters calibtated, I can check them against my plugs.   :-D
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