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Author
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Topic: Just want to get something straight.
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70coupe
Gearhead Posts: 277
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-09-2002 10:01 PM
  
Standard pressure is 29.92" of mercury. When the pressure rises (ie.30.00") higher pressure,does this slow down or speed up your ET. I was under the impression the higher the barometer the higher the pressure the better the air? Do I have this backwards?
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Moneymaker
Administrator Posts: 18704
From: Lyons, IL, USA
Registered: May 99
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posted 09-09-2002 10:12 PM
You are correct.  ------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator NHRA/IHRA/SRA/MCA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl Quote: "I never met a magazine mechanic I liked."
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-09-2002 11:33 PM
Yep,Of course he's right.  Higher barometer equals denser air which means more oxygen molecules in the air.
Lower humidity also equals more oxygen in the air(less water vapor), and lastly lower temp means more air density/more oxygen per cfm of air. SteveW
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Big D
Gearhead Posts: 3286
From: WELLS, NEVADA
Registered: Nov 2000
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posted 09-10-2002 01:15 AM
 Are you sure Professor Steve... Don
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kid vishus
Gearhead Posts: 3894
From: middle of NC
Registered: Oct 2000
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posted 09-10-2002 11:07 AM
Aad the best is high barometer, low temperature, and low humidity all at the same time. yeah, like that happens in the summer.  But that's what the fall is for.
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TomP
Gearhead Posts: 4637
From: Delta BC Canada
Registered: Dec 99
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posted 09-10-2002 12:21 PM
i dunno about that low humidity one... my car has always run it's fastest in cool fog... 100% humidity.We've had air 1000-1500ft below sea level on those occasions.
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Moneymaker
Administrator Posts: 18704
From: Lyons, IL, USA
Registered: May 99
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posted 09-10-2002 12:37 PM
You don't count Tomp! You are Canadian!
You guys also have a "metric" humidity level. ------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator NHRA/IHRA/SRA/MCA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl Quote: "I never met a magazine mechanic I liked."
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 01:06 PM
Tom,I guess you can only have two out of three up north. If you could get all three factors right you'd be in -2000' da. SteveW
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70coupe
Gearhead Posts: 277
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-10-2002 03:18 PM
So,if our track elevation is 600' and the barometer is 29.92" (not factoring in humidity and temp) then the altitude is 600'.
If the barometer goes to 30.02" then the corrected altitude is now 500'. Now that I have that straight. How do we factor in temp and humidity? I did a search but I'm still not completely comfortable. Anyone want to try. Maybe would could make a table that could be printed out for the track for those of us not wanting to pay $500 for a meter.
29.82" = 700
29.92" = 600
30.02" = 500
30.12" = 400
or is there a simple factor that you can multiply or divide the temp and humidity by?[This message has been edited by 70coupe (edited 09-10-2002).]
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kid vishus
Gearhead Posts: 3894
From: middle of NC
Registered: Oct 2000
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posted 09-10-2002 03:31 PM
I dont know. I bought a used ET predictor a few yrs back that does all that for me. It was $250 and works pretty dang good.
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 04:23 PM
Here's my old thread before I broke down and bought a weather station. https://mustangsandmore.com/ubb/Forum12/HTML/002531.html SteveW
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 04:28 PM
From my old thread,Air Density and Performance (Courtesy: Roger Copeland) The Standard Day (SAE test standard J1349): 100% Air Density Temperature: 60 deg. F Humidity: 0% Barometer: 29.92 Barometer
Barometer readings have a linear effect on air density. If the barometer goes up or down 1% from the standard reading, so will air density.
Example:
30.22 (New) ? 29.92 (Std.Day) = 1.01 or 101% 29.62 (New) ? 29.92 (Std.Day) = .989 or 98.9% (Round up to 99%) A barometer of 30.22" gets you to 101% air density, 29.62" nets to 99%, etc. Each 5 deg. F change in temperature (away from 60 deg. F), you get about a 1% change in air density. An 80 deg. F day means 96% air density, and a 40 deg. F day means 104% air density. Temperature goes up... The air gets thinner. Temperature goes down...Air gets thicker. (Air Density) This is not linear, but it's close enough for racing considerations. Ever notice how much better an engine runs on a cool damp day? At 60 degrees, jumping from zero to 50% humidity will cost you roughly 1% in air density. That same 50% humidity at 90 degrees will cost you more than 2% in air density. The reason for this is that it requires much more water vapor to get you to 50% humidity at 90 degrees than it does at 60 degrees, since air can hold more water as it's heated. "Relative humidity" is expressed as a percentage of water in the air compared to how much it can hold at a given temperature. All 3 figures need to be considered. A 50 degree day with 50% humidity and a 29.62" barometer nets you to just about 100% air density, since the 2% you pick up in temperature is offset by the losses from the barometer drop of 1% and the humidity loss of 1%. Power
Figure around 75-80% power change compared to the air density change. An 8% drop in air density will cost you about 6% in power. Barometric changes give you about a 1.2:1 change in power.
Temperature changes give you about .7:1 change in power.
Humidity is about 1-1 change in power. SteveW
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70coupe
Gearhead Posts: 277
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-10-2002 08:57 PM
Hey Steve, I just spent the last 3 hrs making up a spreadsheet for the track. I used that link that you had posted. It should work as well as a computer but a little slower. Oh well, not like you dont have enought time sitting around at the track to figure out a few calculations.
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 09:02 PM
Very cool!Can you post it? Or e-mail it to SteveL for publishing as an article? SteveW
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70coupe
Gearhead Posts: 277
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-10-2002 10:10 PM
After all the help you guys have given me,no problem! I'll take it to work tomorrow and scan it. Then I'll try to post it or email it to you. I've got every other degree from 61 to 79F done so far but will do more over the next few days.------------------
351c 4v clsd heads
60'1.619
1/8 [email protected]
1/4 [email protected]
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 10:22 PM
Great Brian,Got your e-mail, what program is it written on? Maybe I can open it at work tomorrow.
SteveW
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70coupe
Gearhead Posts: 277
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-10-2002 10:23 PM
It a program called Ability Office 2000. Its not a very popular spreadsheet. Let me know becuase I will still scan it at work tomorrow.
Brian
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-10-2002 11:34 PM
quote:
Originally posted by 70coupe:
It a program called Ability Office 2000. Its not a very popular spreadsheet. Let me know becuase I will still scan it at work tomorrow.
Brian
OK, Please do, I'll forward it to our leader. SteveW
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Ryan Wilke
Gearhead Posts: 1115
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 09-11-2002 09:18 AM
How do these conditions sound to everyone???? Today's Forcast:
Mostly Sunny. Barometric 30.05" & rising.
@ 4pm, 72F @ 45%RH.
@ 8pm, 63F @ 66%RH. Do ya think I'll be at Test n' Tune tonite???
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Ryan Wilke
Gearhead Posts: 1115
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 09-12-2002 05:07 PM
quote:
Originally posted by Ryan Wilke:
...these conditions.....Do ya think I'll be at Test n' Tune tonite???
Folks were running hard last night!! ...I saw a BBC '68 Chevelle pull the biggest wheelstand I've ever seen,,,I'm saying over 5ft high!! You could see the whole fuel tank! The 're-entry' resulted in blowing out a front shock mount and pan-caking the oil pan (while goughing a hole in the track!) but after returning to tera-firma, he got back on 'er and ran a 10.68... ...I talked to the fella after; he said it normally lifts 1-2ft,he stays on 'er without any problems. But he's never had it go THAT high before! Too Bad no one got a pic of it!!!!
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TomP
Gearhead Posts: 4637
From: Delta BC Canada
Registered: Dec 99
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posted 09-12-2002 08:09 PM
A pet peeve of mineNobody ever gets pictures when i do decent wheelies... and somehow i manage to miss getting shots of anybody elses 
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