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Effect of Weather on ET

ksurfer2

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How much of an impact does an increase in Temperature/humidity have on ET? Let's say my car can run and 11.20 @ 117 when it is 70 degrees out and low humidity (winter in FL), how much of a hit will I see when I run on a 90 degree high humidity day (summer in FL).
 
Barometric Pressure will play into that as well. Good Luck
 
Best answer i can give: start playing around on Wallace Calculators. He has formulas that directly address this. Be prepared with weather info.

My completely wild-assed guess, would be... youll slow down a couple tenths, and 1-2 mph. Maybe more.
 
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A lot! Don't you remember when Elliot took him out on Halloween? Exposure to the weather damn near killed him.
 
I could never figure out what's worse, when it's 90 degrees the slicks bite really good
and you can come off the line a little hotter. As long as the humidity is not over 70%
it's not too bad, but when it's chilly willie the car doesn't hook up. Humidity does play
a part, but jeez, there's so many variables! We just wanted to have fun.
 
I just want something to blame bad time slips on. It CAN'T BE my tuning or driving!!!
 
You'll probably get 50 different answers. Some combinations are effected by heat, some by humidity, some by barometric Pressure
I would say get a good weather station, or download this on your phone
https://airdensityonline.com If your race track is on here then you'll find it's really accurate. ( we checked it with a weather station and it was spot on)
Start logging your ET along with the weather and you'll start to see a pattern.
 
Keep a log. Water grains, density altitude, temperature....they all affect power.

Mine is a pig on hot, humid days when running n/a. Up to .3 difference! I thought something was wrong the first time I ran the car in those conditions and it was so far off!
 
I'm no expert, but I have had my best times around Easter time....for us that means summer is mostly gone, the air is drier and cooler, there is still good heat in the track from the sun, and there is usually little wind resistance.

So I'm picking that would be around October for you guys. :thumbsup:
 
Performance 101,
sort of generic

as long as track temps
(not the air temp)
are above 70*f & below 120*f
(usually air temp less than 85*f or above like 55*f)
altitude make track surfaces heat up quicker too
(closer to the sun)

RAD (relative air density corrected altitude) corrected altitude
combined barometric pressure & altitude/elevation combined
is below 2500-3500ft altitude/elevation (marginal air)
between 90 grains of water per million & like below 120-ish/gpm
higher end it shouldn't be too bad, 1-3 tenths loss possibly,
depending on HP levels
the closer to full-on race combo, more on the edge,
the more it will be noticed

more RAD/corrected altitude/elevations = less power

you can tune some of that back in,
when the Altitude/elevation goes up
the BTDC timing goes up
Altitude/elevation up
the carb jetting goes down smaller #'s (leaner)
(with FI {especially mech. FI}, you bypass more fuel off to lean it down)
altitude/elevation goes up
compression goes up (thinner head-gaskets or even camshaft timing)
& visa versa
good air lower altitudes
bigger #'s jetts with good air & smaller bypass pills in FI
(fatten it up)
back of timing a lil' too, usually several degrees (like 3-4*'s)
(even can take away some compression, thicker head gaskets,
not really necessary in some/most cases, depending on fuels used etc.)

blown combos you need more overdrive %
'spinning the blower faster" than the crankshaft by %
a smaller pulley on top &/or a larger pulley on the bottom
makes more boost
thinner head gaskets & more compression helps too
the air is thinner, it will starve for air, timing & compression

chutes will deploy slower too, lack of air molecules

turbo cars don't like to spool up at severe altitudes,
you need or could use N2O (or CO2) to help it spool faster

just because you're at 1500' base 'actual altitude
doesn't mean the RAD air is at that range,
you can have a 3,000 to 5,000 ft
RAD change, up or down, it is most often much higher/up (RAD)
with less air, more grains of water
it's not often less than altitude/elevation than your actual altitude
but;

sometimes at or near sea level tracks, it can be below sea level
& when it is that's mineshaft air, really good air
better air, better tracks mostly too
usually comes with some cloud cover & cooler air temps,
far less humidity
it's really really good air for making HP
'at that specific altitude' that day

even more, noticeable if you race at someplace like
Morrison Co. Bandimere Speedway, with a base altitude of 5800+ ft
I've raced there when it was RAD corrected altitude at 12,000ft
The car/engine feels like a turd, seriously down on power
even with timing in it & leaning it out & more compression

Roots or centrifugal Blower can overcome some of it,
but even they will be slower

N2O cars like cool weather, you need to keep on-top of the bottle temps
make sure it's a constant 900-950psi, no matter the outside temps
either warm it up to raise the bottle pressure
or cool it down to decrease the bottle pressures

you really need to start keeping a log of what the conditions are
when & where, refer back to them for tuning
Wall of text -bob the builder-.jpg
 
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Around here.......On the dyno, the difference between “decent” air(not killer mineshaft air), and hot, humid summer air is about 5% in correction factor.
So, in decent air..... the HP correction factor will be 3-5%.
In hot, humid, summer air, it’s mote like 8-10%.
So, on something making 600hp(corrected), the motor will lose about 30hp from “normal” air, to hot humid “summer” air.

When the air is really good here the correction will be close to “0”, and every once in a while the correction will go ever so slightly the other way(corrected power is lower than uncorrected power).
 
I run roughly 100 passes a year in various weather. Usually in the middle of the summer it'll slow about 2 tenths. This year only two outings and it has varied from 9.05@148 down to 9.24@144. We've had some unusually poor weather for his time of year. like 1.096 correction. The highest barometer so far has been 28.6. Last time out 8-10 mph head wind as well. Barometer, vapor pressure density altitude, and wind are the biggest factors in my book.
Doug
 
Is there a time in the run where bad air will have a bigger impact than others? For example, will bad air have more of an impact on 1/4mile ET/MPH than it will on 60' times, or 1/8mile times/MPH? Or will the bad have have an equal impact on the entire run?
 
How much of an impact does an increase in Temperature/humidity have on ET? Let's say my car can run and 11.20 @ 117 when it is 70 degrees out and low humidity (winter in FL), how much of a hit will I see when I run on a 90 degree high humidity day (summer in FL).

If you jet the carb on the lean side I'd say less than a tenth
 
Temp, baro pressure, and water vapor impact hp, but not wind. But temp can help traction. So you cannot necessarily say where the car might be effected the most, as it depends.

You could see 3 tenths and 3 mph depending on how different the two extremes are. And as someone mentioned, If you running a little rich in good conditions (low temp, low humidity, high baro), you're change will be bigger in poor conditions.
 
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