Let’s have a good track weather (bar, temp, humidity, corrected altitude) discussion

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pittsburghracer

pittsburghracer

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A member asked me this question today about the scribbling I do on my time slips.

Hi John, looks like it was a great night of racing with a good turnout! I notice that you write the weather info on your time slips. Are you using a weather station? Personally I view those as voodoo magic! My question is, in a nutshell, how does density altitude affect performance? I know with high humidity you should jet up to compensate for the increased moisture in the air, and vice-versa, but I don't have a clear understanding of how DA affects performance.

We have all been at the track and said man it feels “fast” tonight. Why is this??? Someone added if the adjusted alt is lower it’s faster. Well here’s three time slips from Saturday that blows that theory out of the water. Join in guys and let’s discuss this. I have some saved material I will try to add if there’s interest in this subject. I usually try to catch the time and time trial or eliminations in the pictures. Gotta head to the shop but I’ll check in later.

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Bobzilla said:
I don't remember if you ever mentioned it, but do monitor transmission fluid temperature?
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Yes I do. I dont go enough rounds to worry about it but I monitor it on my RacePak. Many of my friends run a Bob Jones cooling pump system to keep temps cool. Bob is a Keystone racer.
 
Actually, when humidity goes up, you need to jet down (go leaner). The reason being is that higher humidity means there are more water molecules in the air which displace oxygen molecules. Water doesn't burn and with less oxygen available, you need less fuel to maintain an optimum A/F (air/fuel) ratio to make the most HP.

Similar situation with altitude. The higher you go up (i.e.: Mile High nationals), you have to jet leaner because the thinner air offers less oxygen.

With less oxygen available and leaning the carb to maintain the best A/F ratio, you will make less HP overall. But maintaining the best A/F ratio you can will provide the most HP using the oxygen that is available.

DA gets more complicated.

I used an Altronics PerformAIRE ECLIPSE during my years running with IHRA and found it very helpful. Just gotta make sure you put the most accurate data possible so it can provide accurate predictions. One minor driver, mechanical or weather "difference" in a run will affect the data. (i.e.: tire slip, launch RPM, shift points, wind/breeze strength & direction, engine water temp., tire pressures, stage position, etc.) When you are sure you make s run with the minimal amount of variation, you put that in. (The weather station takes care of the weather side of things.) I entered the wind and direction the best I could manually with a separate wind meter. Walls, bleachers, etc. can cause some inaccuracies there due to blocking & swirling.

Weather stations/predictors are expensive but keeping accurate records any way possible can help you find patterns and help predictions.
Some quick weather changes can fool you or the weather station. Sometimes you can just "feel" the air get better or worse. Not 100% fool-proof, but it helps.
 
Thank you for doing this. I was trying to do a layman's description on Johns other post.
Using a inexpensive weather station,using the DA chart aircraft pilots use, and chart temp,pressure and humidity.
I have been out of the racing game for awhile. Just a bit fuzzy. For bracket racing you try to do the same every run for consistency .Wind direction and speed,Engine temp,Tire pressure and the like.

I was old school and used a on-off switch for my electric waterpump to be at the same temp every run when at the tree.
 
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I know high temps and humidity effect carburetors I suppose its air density but how about traction is a blacktop that is baking in the sun more or less for traction...?
 
I'm going to try to learn what you guys say, my track is in the desert at 1100 altitude, always hot not much humidity.
 
MOPARMAGA said:
I'm going to try to learn what you guys say, my track is in the desert at 1100 altitude, always hot not much humidity.
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We are 1200 feet. That’s why you coastal tracks are .10 quicker from the get go. Very common for them to see -600 feet so the test n tuners head out in the Fall for new bests and a bragging number.
 
pittsburghracer said:
We are 1200 feet. That’s why you coastal tracks are .10 quicker from the get go. Very common for them to see -600 feet so the test n tuners head out in the Fall for new bests and a bragging number.
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The big national event track "Pacific raceways" formally Seattle international raceway is pretty low altitude and plus has Coastal air. I think boosted and his demon at .300 quicker than my track.
 
Pacific 310 ft
Spokane 2300
Walla Walla 1160
Firebird/ Boise 2700
MOPARMAGA said:
The big national event track "Pacific raceways" formally Seattle international raceway is pretty low altitude and plus has Coastal air. I think boosted and his demon at .300 quicker than my track.
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Most of that is above my pay grade, but I do know that cool, dry air makes um run fast.
 
I figure .10 approximate loss for every 1000 foot on gas. I know their altitude is super high out there but what’s the humidity like. That crazy weather at Quaker City a few weeks ago that I had to dial a 6.15 was terrible. My sweat was sweating.
 
When I last raced (in the 90's), some guys swore by their e.t. predicting devices (anything from the temp/baro/hygrometer gizmo on the living room wall, to whatever the lastest hi tech gizmo was), and some swore at them.
We did record weather info (we used a buddy's "weather station"), etc. in a logbook, and never saw a dependable pattern.

As a result, my partner and I could never decide what to buy. Instead we used to watch the first few pairs, and see if more cars were breaking out, or more cars couldn't run their number, and dial accordingly.

Is there a good predictor these days, or is this like asking what oil is good?

I kick around the idea of racing my Duster, but with the loss of Atco, I'll have to go to Cecil County, my only real choice, as I live waaaaay down in southern New Jersey. I'll have to see what that drive is like.
 
Thank you for posting this information John! It's very interesting reading and has answered the questions that I had formulated in my CRS riddled mind!
 
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